Martin Ritt, a director admired for making films that explored moral choices and reflected concern for racially and economically oppressed people, died on Saturday in Santa Monica Hospital Medical Center in California. He was 76 years old and lived in Pacific Palisades, Calif.

The film maker died of heart disease, a family spokesman said.

Beginning in 1957, Mr. Ritt directed and occasionally co-produced 25 diverse films, including "Edge of the City," "The Long Hot Summer," "Hud," "The Spy Who Came In From the Cold," "Sounder," "Pete 'n' Tillie," "Norma Rae," "Murphy's Romance," "Nuts" and "Stanley and Iris."

Most of his films were quietly moving studies of human relationships, punctuated by periodic hits that gave the husky, tough-minded director freedom to deal with social issues and the alienation of outsiders. 'The Human Condition'

Critics argued that his idealism made some of his work sentimental and susceptible to sugar-coated themes and happily-ever-after endings. In rebuttal, he said in 1986 that "most of my pictures are concerned with the human condition."

Speaking in the gravelly rhythms of the Lower East Side of Manhattan, where he grew up, he added, "I'm also very committed to assuming responsibility for one's actions." The concern, he said, was rooted in part in his experience of being blacklisted in the 1950's for past Communist ties. He bitterly skewered the era in his 1976 film "The Front."

Mr. Ritt was known as an actor's director who enhanced many careers and was widely admired, although he was nominated for an Academy Award only once, in 1963 for "Hud," an incisive character drama that won Oscars for Patricia Neal, Melvyn Douglas and the cinematographer James Wong Howe.

"I make the kind of films that not too many people get to make in this town, though sometimes I've had to take the risk myself," he said in 1986. To make both "Sounder," a 1972 tale of black sharecroppers during the Depression, and "Norma Rae," a 1979 story about a struggle to unionize a cotton mill in the South, he said, he and most of the principals worked for far less than their normal salaries, in exchange for a percentage of any profits, which were ultimately considerable. An Unobtrusive Hand

Mr. Ritt directed his camera the way he directed actors, with restraint, favoring a linear, sequential technique and eschewing flashy camera angles and shots and editing. "I don't use the zoom unless that's the only way I can get into a scene," he once said. "The audience shouldn't be aware of the director's work until the movie's over."

Martin Ritt was born to immigrant parents in Manhattan on March 2, 1914. He graduated from DeWitt Clinton High School in the Bronx and Elon College in North Carolina, where he was a running guard and a boxer. He began studying law at St. John's University, but he met and befriended Elia Kazan and joined him in New York's Group Theater, where he acted in "Golden Boy" and other socially conscious Depression-era plays.

He served in the Air Force in World War II, appearing in the service's stage and film drama "Winged Victory." After the war, he acted in live television plays but increasingly stressed directing. He was then blacklisted for five years and eked out a living by teaching at the Actors Studio.

He began film directing in 1957 with "Edge of the City," a powerfully realistic waterfront drama with racial overtones and starring John Cassavetes and Sidney Poitier.

Mr. Ritt is survived by his wife, Adele; a daughter, Martina Werner, a film producer, of Los Angeles, and a son, Michael, of Alaska.