Henry Ford 2d, who took over the ailing auto company founded by his grandfather and restored it as one of the world's industrial giants, died yesterday in Detroit of complications arising from pneumonia. He was 70 years old.

''My name is on the building,'' Mr. Ford used to say to settle arguments. It was on more than that; Ford was possibly the best-known name in the world.

Each day it was stamped hundreds of thousands of times on metal, and it glistened in neon and in chrome at Ford plants from Detroit to Dallas, from Dagenham in England to Valencia in Spain, from Port Elizabeth in South Africa to Taipei, Taiwan. Even in the Soviet Union and China, Ford meant cars. Committed to Car-Building

Mr. Ford never forgot that. The hundreds of millions of dollars in his personal fortune could have bought a life of leisure, or at least one of high-class philanthropy. Mr. Ford enjoyed both, but first, last and always, Henry Ford 2d built cars.

Mr. Ford fell ill while visiting Germany in August and returned to the Detroit area on Sept. 5. He had been in intensive care in the hospital named for his grandfather, Henry Ford, since Sept 14.

Lee A. Iacocca, who was dismissed by Mr. Ford as president of the Ford Motor Company in 1978, was one of many associates and competitors who praised the man who symbolized and managed the company for 34 years.

''His vision and hard work transformed Ford into a great company,'' said Mr. Iacocca, now the chairman of the Chrysler Corporation. ''Henry Ford and I were friends and colleagues for a lot longer then we were adversaries.'' Not an Early Bird

Henry Ford was not one to show up at the office before the crack of dawn. ''I hate to get here before 9 o'clock,'' he said. ''That just kills me. Some people have metabolisms that get to work early; some people have metabolisms that don't get to work until later on.''

But when he got to the office, he was in charge, and good men were let go because they did not quite understand that. ''I'm probably standing in the way of a lot of people,'' he said. By 1979 he was ready to relinquish some power and resigned as chief executive. He remained as chairman until 1980 and was chairman of the board of directors' powerful finance committee until his death.

Like his grandfather, Mr. Ford, as he grew older, guarded his power jealously and eliminated those aides who came too close to it.

He also emerged as a social reformer, using his heritage and prestige in the cause of equal opportunity and leading the effort to rebuild Detroit. And at the same time, he became known as a man who enjoyed the company of women. Because of his name, any known liaison became news. ''Never complain, never explain,'' Mr. Ford once said, after he was arrested for drunken driving.

What would be his life's work was settled at his birth, and by the time he was 28, he had made it to the top.

World War II had just ended when Mr. Ford, backed by his mother and a few allies, seized control of the company. By then his grandfather was probably senile. His grandfather's only son - Henry 2d's father, Edsel - was dead, and one by one, Ford's most competent executives had been dismissed.

The company was losing almost $9 million a month and approaching ruin despite its giant size, and the senior Henry Ford seemed to be turning over control to an aide, Harry Bennett, a pistol-carrying personnel chief.

When the younger Mr. Ford found out about a secret document that would give Mr. Bennett control, he threatened to quit, saying, ''If I do, I'm going to write a letter to every dealer in the United States and tell him just what kind of a situation he's associated with.'' The Ford Women Act

Eventually, Mr. Ford's grandmother, Clara, put pressure on her husband, and Mr. Ford's mother threatened to sell her stock in Ford, which was then family owned, unless her son was given control. In September 1945, the 82-year-old Mr. Ford resigned, and his namesake took over.

The first thing he did was to discharge Mr. Bennett personally. ''You're taking over a billion-dollar organization that you haven't contributed a thing to,'' Mr. Bennett angrily told Mr. Ford.

Once Mr. Ford won control, he began rebuilding, hiring good men and, to his credit, listening to their advice. The saving of Ford Motor was the business miracle of the decade; those who knew the situation said the company was not just dying, it was already dead. But Mr. Ford had pluck and luck.

''I never had any doubts that it could be done,'' he said later. ''Maybe that was the naive opinion of a young fellow who didn't see any reason that, with a little hard work and the help of a lot of good people, it couldn't be turned around. The world was our oyster and we were going to make an indent one way or the other, and we were all full of vinegar and we were going to go at it, whatever happened.'' Two Auto Landmarks

Along the way, Ford created two of the most recognizable models in auto history - the trim sporty Thunderbird of the mid-1950's and the Mustang developed by Mr. Iacocca in the 1960's.

Even pluck and luck, however, were not enough to help Mr. Ford achieve his greatest goal: He could never overtake the family's decades-long rival, the General Motors Corporation. By 1960, with the failure of the Edsel model, which had been aimed at the buyers of medium-priced cars, the heart of the G.M. market, the dream dimmed.

Foiled at home, Mr. Ford expanded aggressively overseas, establishing Ford as a major power in Europe and elsewhere. Like the other American car companies, Ford was stunned by the oil crisis in 1973 and the flood of fuel-efficient Japanese imports that followed in its wake. Mr. Ford never did like small cars, but he approved the development of smaller models such as the Fiesta in Europe and the Pinto in the United States. With characteristic brashness, he predicted in 1978 that they would drive the imports ''back into the sea.''

They did not, of course, but under Mr. Ford's direction, Ford bought a 25 percent interest in the Mazda Motor Company. That provided access to Japanese technology and low-cost parts as well as to the development of hybrid Ford-Mazda cars sold in overseas markets as Fords. An International Influence

By the time Mr. Ford was ready to step down, he had embedded an international viewpoint at Ford by naming to top positions who had done well in overseas assignments.

Mr. Ford finally had the satisfaction of watching those he put into power best G.M., at least in a financial sense. In 1986, with Mr. Ford still exercising power behind the scenes on the finance committee, Ford reported profits of $3.3 billion, to G.M.'s $2.95 billion. It was the first time since 1924 that Ford had beaten G.M. on the bottom line.

The success of Ford's recent models, particularly the aerodynamic Ford Taurus and Mercury Sable, enabled the company to recapture some of the share of the American car market it had lost in the early 1980's.

After Mr. Ford's palace coup brought control of the company, it took 10 years of hard work to rebuild Ford Motor into an industrial power throughout the world. In 1956, the family company sold stock to the public. Yet it was structured so that the family - which meant Mr. Ford, as it had meant his grandfather - maintained control. Complex Personality Emerges

Only after the company was re-established did other sides of Mr. Ford's character begin to emerge: the social thinker; the party-goer; the autocrat.

His grandfather had been known for his social involvement, for the famous $5-a-day wage that caught the imagination of the working man, for his efforts to uplift the lives of the working class, for his Peace Ship mission to Europe to try to end World War I, and for his readiness to give jobs to blacks when segregation was a way of life in America.

But as Henry Ford aged, his idealism soured. Union organizers at Ford were beaten, workers were spied on, his pacifism became associated with anti-Roosevelt, pro-German feelings as World War II approached, and his friendly attitude toward blacks was matched by his hatred of Jews.

But the grandson wiped bigotry and anti-labor activity from the Ford image. And when racial riots flared in the 1960's, Henry Ford was the outstanding business spokesman calling for a new deal for blacks, particularly after the Detroit riot of 1967. Pioneer on Racial Policies

He forced the creation of the National Alliance of Businessmen to work toward solving the problems and led the way in changing hiring, promotion and dealer-selection practices that had kept blacks out of Ford's plants, offices and showrooms.

His interest in these social problems seemed to fade as the years went on, particularly when individual efforts were replaced by Government orders and programs.

But he also created, with his company's money and his personal prestige, the Renaissance Center, a major development on the Detroit River. A decade later the center, while it has had financial problems, nevertheless was the focus of renovation and development up and down the once grimy waterfront.

And Mr. Ford oversaw the creation of the modern Ford Foundation, dedicated to curing social ills and transforming society, and served as its chairman from 1950 to 1956. At first he stood up for the foundation's liberal efforts, but he lost control of the board and finally, in 1977, quit in disgust, complaining that it had an anticapitalist bias. Personal Life Becomes News

Mr. Ford's social life became newsworthy as his marriage to Anne McDonnell, the mother of his children, faded in the late 1950's, particularly after he met Cristina Austin, the divorced wife of a British naval officer. In 1963 Mr. and Mrs. Ford separated and in 1964 they divorced; a large settlement was believed to be involved. In 1965 he married Mrs. Austin.

Mr. Ford had become a member of the jet set and was seen from Acapulco to the Riviera. He was spotted squirting seltzer at an Italian count who happened to be in a tree at a party on the Riviera, and he was linked to numerous other antics.

''He has a darn good time when he has a good time,'' said his brother William Clay Ford, the owner of the Detroit Lions football team. But it was a Detroit-style good time, nothing fancy. ''His idea of fun,'' his daughter Charlotte said, ''is going out and having a few drinks and being sort of loud.''

''He always loved ending up in the pool with his clothes on,'' she said. ''That was his idea of breaking away from tradition.'' Erratic Behavior

After a decade with his second wife, Mr. Ford moved out of their lakefront mansion.

He grew a beard and drank heavily, and his behavior became widely known when he was arrested and charged with drunken driving in California while with a Detroit friend, Kathleen DuRoss, whom he married in October 1980 after a second divorce. He then appeared to pull himself together, shaved the beard, curbed the drinking and was back at work running his company.

The late 1970's were difficult times. Colorful uncomplimentary stories about the personal lives of Mr. and Mrs. Ford appeared in the press. A group of stockholders sued, represented by Roy M. Cohn, who was also Mrs. Ford's lawyer, charging that Mr. Ford had taken bribes and used company money as his own. The suit was later dismissed. There were troubles with Ford cars: Pintos that burned, automatic transmissions that shifted into reverse by themselves, bodies that rusted. And the mighty challenge from Japan. Frequent Conflict With Aides

At the same time, Mr. Ford's desire to keep his power brought him into conflict with his aides - a situation not unlike that in his grandfather's day. For whatever Mr. Ford's outside interests might have been, the company was his life and his kingdom.

''He's got nothing to do outside the company,'' his son Edsel 2d once said. He hunted ducks a bit, tried golf and was not much on skis. It was his office on the 12th floor of the Glass House, as they call the Ford headquarters in Dearborn, Mich., outside Detroit, that was his home.

And anyone who even unknowingly challenged him there had to go.

There was Ernest Breech, brought in by Mr. Ford to rebuild the company. After a decade Mr. Ford told Mr. Breech, ''I've graduated.'' Mr. Breech, one of the most competent of American businessmen, understood and left. A Friend Is Dismissed

There was Semon (Bunkie) Knudsen, a personal friend and millionaire whom Mr. Ford hired from General Motors to run Ford. But when Mr. Knudsen tried to run Ford as he would have run General Motors, Mr. Ford, unwilling to give up power, dismissed him in 1969 after 19 months. ''It just didn't work out,'' he said.

Ironically, it marked the second time in history that a Ford and a Knudsen had parted. Mr. Knudsen's father, known as ''Big Bill,'' had been a Ford executive in the 1920's and was forced out. He went to General Motors and built Chevrolet into a champion, became G.M.'s president and headed the mobilization effort of American industry in World War II.

A decade after the younger Mr. Knudsen was discharged, Mr. Ford struck again, dismissing another president, Lee A. Iacocca.

Mr. Iacocca had worked his way up in the early 1960's and led the Ford recovery from the Edsel debacle by creating the car that caught the imagination of a decade: the Mustang. He had been a leader in the conspiracy to topple Mr. Knudsen, and once at the top appeared to play the role of the loyal prime minister, never threatening the power of the monarch himself. It did not save him. Just 'One of Those Things'

''After 32 years, he just said it was one of those things and he hated to do it but he had to do it,'' Mr. Iacocca said the night he was discharged. ''He doesn't want strong guys around.''

Mr. Iacocca later bitterly attacked Mr. Ford in his autobiography. Mr. Ford did not respond.

A few months later Mr. Iacocca was running the troubled Chrysler Corporation, trying to do to Henry Ford 2d what William Knudsen had done to Henry Ford a half-century before. Mr. Iacocca pulled Chrysler from the brink of bankruptcy.

After the Iacocca dismissal, self-preservation became the order of the day at Glass House. But Mr. Ford let the word out that he might retire a few years early, before he was 65. That brought home sharply the question of succession. A Change of Command

At the annual shareholders meeting in 1979, Mr. Ford said he would retire as chief executive. He said his successor would be Philip Caldwell, the company's president and deputy chief executive, the first time a someone from outside the family would run Ford. When Mr. Caldwell retired in 1985, he was replaced by Donald E. Petersen, and the tradition of nonfamily rule was established.

Roger B. Smith, the chairman of Ford's principal rival, the General Motors Corporation, observed yesterday: ''In a very real sense, eveybody in the auto industry is part of the same family, sharing the same dreams and challenges and fighting the same battles in the competitive arena that is today's marketplace. That family lost one of its leading members today.''

And Owen F. Bieber, the president of the United Automobile Workers union, termed Mr. Ford ''one of the most influential and colorful figures in the auto industry,'' adding, ''During the time he headed the company, the U.A.W. was able through negotiations at Ford to introduce important new concepts that subsequently set industrywide standards.''

Edsel Ford 2d, the sales manager for Ford's Lincoln-Mercury division, said yesterday that the family supported the current management of the company and planned no changes. One of Four Children

Henry Ford 2d was born Sept. 4, 1917, to Edsel and Eleanor Ford. He was the eldest of four children; there were two brothers, William Clay and the late Benson Ford, and a sister, Josephine.

He attended the Hotchkiss School in Lakeville, Conn., and Yale University, but did not graduate from college.

Mr. Ford became a director of the company by 1938 - at 21 - and his first job at Ford was as a mechanic in the dynamometer room at the Rouge works in Dearborn.

He became a Navy officer in 1941, but in 1943, after his father, Edsel, died, he was returned to civilian life to help run the Ford factories.

Mr. Ford is survived by his third wife, Kathleen; his son, Edsel 2d, and two daughters, Charlotte and Anne; six grandchildren, his brother William and his sister Josephine.

Funeral arrangements were incomplete. Edsel Ford 2d said a private family funeral was planned, followed by a public memorial service in two to three weeks.