Ted Sorensen, the admired longtime assistant to President John F. Kennedy who provided his chief with many of the words and thoughts that still resonate through American life, died Sunday at New York Presbyterian Hospital of complications from a recent stroke. He was 82.

Of those before and since who have served any American president, none has been given greater credit for their contributions to an administration or its legacy than Mr. Sorensen.

N

o aide in recent times has had more influence on a president's message or on how it was expressed, said Princeton University historian Sean Wilentz.

Amply endowed with the qualities required for an intimate adviser at the highest levels, Mr. Sorensen was regarded as a man of ideas and ideals, keen intellect and a passion for public service.

From Mr. Sorensen - or from his close and fruitful collaboration with his president - came the words by which Kennedy called on the nation to achieve such goals as placing a man on the moon and providing civil rights to all Americans.

"Sorensen," historian Douglas Brinkley wrote two years ago, "was the administration's indispensable man."

The image of the Kennedy administration as an American Camelot, presided over by the wise, graceful and just, can be traced in considerable degree to Mr. Sorensen's alluring language, through which the administration presented itself.

A master of the craft of transforming sweeping vision into strong verbs and nouns, Mr. Sorensen also was the soul of discretion, always loyal to his president and ever ready to deflect credit from himself.

Mr. Sorensen went on to a long and productive career after Kennedy was assassinated. He served as a speechwriter to President Lyndon B. Johnson and aided in the campaigns of several prominent Democrats, including Sens. Robert F. Kennedy and Gary Hart. Mr. Sorensen made a reputation as an international lawyer and spoke out on behalf of liberal causes.

He was an early endorser of the presidential candidacy of Barack Obama, and the president issued a statement Sunday praising Mr. Sorensen for his quick wit, seriousness of purpose and determination to "keep America true to our highest ideals." Mr. Sorensen, Obama said, led an "extraordinary life" that inspired many and helped make America and the world "more equal, more just and more secure."

Although he became identified with the rhetoric with which Kennedy defined himself and his policies, the studious Mr. Sorensen, seemed satisfied to be behind the scenes, working under the title of Special Counsel and Adviser and accepting whatever reflected glory came to him.

"It isn't all that important who wrote which word or which phrase in Kennedy's inaugural," he once told an interviewer. "What's important are the themes and the principles he laid out."

Many memorable speeches during the thousand days of the administration showed Mr. Sorensen's handiwork. Recruited to join the small group that advised the president during the Cuban missile crisis of 1962, which brought the world to the brink of nuclear war, he helped craft the president's correspondence with Soviet leader Nikita Khrushchev. The meticulous wording was viewed as vital in bringing about a satisfactory resolution.

Mr. Sorensen also played an important part in drafting the president's first speech to the nation on the crisis. Another speech with which Mr. Sorensen was identified was given by the president at American University on a sweltering June day in 1963. Calling for a nuclear test ban and a new look at the possibility of peaceful coexistence with the Soviets, Kennedy asked Americans "not to see only a distorted and desperate view of the other side, not to see conflict as inevitable, accommodation as impossible and communication as nothing more than an exchange of threats."

B

orn into a family with a heritage of engagement in progressive politics in Nebraska, Mr. Sorensen joined Kennedy's staff in the 1950s, when the Massachusetts Democrat was in the Senate.

Although different in many ways, the two men bonded, achieving a closeness that made many writers describe Mr. Sorensen as Kennedy's alter ego. Kennedy called Mr. Sorensen his "intellectual blood bank."

Some who reported on the president maintained, perhaps facetiously, that Mr. Sorensen dwelled within Kennedy's mind and was sufficiently familiar with every detail of its workings to enable him to finish the sentences that the president began.

In an interview with the author of a book on White House speechwriters, Sorensen said there was in fact "something to that."

"There's a tremendous advantage for a speechwriter to know his boss's mind as well as I did," he said.

When the president was assassinated, Mr. Sorensen was crushed; he called the events of Nov. 22, 1963, "the most deeply traumatic experience of my life."

Never, he said, had he thought of a future without Kennedy. Over the years, he came to be regarded as one of the principal defenders of the president's legacy.

In addition to literary craftsmanship, Mr. Sorensen was known for his fidelity and circumspection, which were notably on display at key junctures.

One of them involved the famed 1961 inaugural address.

Of all of the presidential speeches of the past 100 years, few have had more lasting impact than Kennedy's inaugural address. In that speech, no sentence is better remembered than the exhortation: "Ask not what your country can do for you; ask what you can do for your country."

Much of the galvanic effect of that speech is credited to Mr. Sorensen. He played a key role in composing the address. But he constantly and firmly maintained that the famous sentence came from the pen of the president.

M

r. Sorensen played an important part in the writing of the book that formed another part of the Kennedy legacy. That was "Profiles in Courage," which won the Pulitzer Prize for history in 1957. How credit should be allocated between Mr. Sorensen and Kennedy was long a subject of controversy.

Mr. Sorensen acknowledged writing a first draft of most chapters and said that he "helped choose the words of many of its sentences."

But when a reporter asserted publicly that the book was Mr. Sorensen's work, he gave an affidavit saying that it was Kennedy who was the author.

Theodore Chaikin Sorensen was born May 8, 1928, in Lincoln, Neb. His father, who became Nebraska's attorney general, was a Republican progressive. His mother, of Russian Jewish background, raised her children in the Unitarian Church.

World War II ended when he was 17; his decision to register afterward as a conscientious objector helped derail his nomination during the Carter administration as head of the Central Intelligence Agency.

After law school at the University of Nebraska, Mr. Sorensen's interest in public service brought him to Washington, where he worked in government and was soon offered a job in Kennedy's Senate office.

In the run-up to the 1960 presidential campaign, they crisscrossed the country together, discovering, as Mr. Sorensen wrote in a 2008 memoir, "Counselor," that they "enjoyed each other's company, joking, talking politics and planning his future."

Of all the aides on Kennedy's New Frontier, wrote correspondent Hugh Sidey, only Mr. Sorensen "seemed to pop up everywhere, doing everything."

Mr. Sorensen later wrote a best-selling biography of Kennedy.

In 1970, Mr. Sorensen sought the Democratic senatorial nomination in New York but lost in the primary.

The stroke he suffered on Oct. 22 was his second. The first, in 2001, diminished his sight so much that he had to dictate his later memoir. His research assistant on the book, Adam Frankel, became a White House speechwriter himself; "He sets the standard," he said of Mr. Sorensen.

His marriage to the former Camilla Palmer ended in divorce.

Survivors include his wife, Gillian Martin Sorensen of New York; three sons from his first marriage, Eric, Stephen and Philip, all of Wisconsin; a daughter from his second marriage, Juliet Sorensen Jones of Chicago; and seven grandchildren. Also surviving is a sister, Ruth Singer of Falls Church, and a brother, Philip, of Columbus, Ohio.

During the Obama campaign, Mr. Sorensen said he was perplexed at the derision of the candidate's addresses as "just words."

" 'Just words' is how a president manages to operate," Mr. Sorensen told the Boston Globe. " 'Just words' is how he engages the country."