Abe Fortas, 71, who resigned as an associate justice of the U.S. Supreme Court in 1969 in the face of accusations of impropriety that scarred a brilliant career in law and government, died of a ruptured aorta Monday at Georgetown University Hospital. He was stricken at his home in Georgetown.

Mr. Fortas, the son of a Jewish pawnbroker and cabinetmaker, was an accomplished classical musician, a New Dealer, a confidant of President Lyndon Johnson, a founder of one of the country's most prominent law firms, and an unsuccessful nominee to be chief justice of the United States.

Long before he became a public figure, he made a notable record for his support of civil liberties when these were put at risk by the virulent anticommunism associated with the late senator Joseph R. McCarthy, a Wisconsin Republican. In 1963, he successfully argued Gideon v. Wainwright, the landmark decision in which the Supreme Court found that all defendants in criminal cases are entitled to lawyers, if necessary at public expense.

Joseph M. Berl, one of his law partners, said Mr. Fortas had appeared in good health recently, enjoying a full social life and working nine-hour days at Fortas and Koven, the law firm he started after resigning from the court.

Mr. Fortas made one of his last public appearances March 22 when he returned to the Supreme Court for the first time in 12 years to argue a case.

He proceeded in his relaxed but meticulous fashion, with many fewer interruptions by justices than is usual in the court, and concluded by telling his former colleagues: "It's been a great pleasure and honor to be here."

Mr. Fortas served four years as a member of the Warren Court's liberal bloc, famous for its rulings on behalf of the rights of criminal defendants, minorities and individual liberty.

However, he spent much of his time defending himself, first from criticism that he was too close to the man who appointed him, President Johnson, and then from conflict-of-interest allegations. His acceptance of $15,000 from wealthy friends and former clients hoping to finance summer university seminars by Mr. Fortas helped deprive him in October 1968 of the legal profession's highest honor, the chief justiceship of the United States. He would have been the first Jew to hold that post.

Seven months later, with congressional animosity already stirred up against him and a new president, Richard M. Nixon, in office, revelations of a financial relationship between Mr. Fortas and the family foundation of Louis E. Wolfson, convicted and imprisoned for securities violations, forced Mr. Fortas to resign from the court. He became the first man to leave the court under fire.

"There has been no wrongdoing on my part," Mr. Fortas wrote Chief Justice Earl Warren on May 14, 1969. "It is my opinion, however, that the public controversy relating to my association with the foundation is likely to continue and adversely affect the work and the position of the court, absent my resignation."

Mr. Fortas was born in Memphis on June 19, 1910. He was the youngest son of William and Ray (Berson) Fortas, who had immigrated from England. His father had a deep appreciation of music and learning, which he passed on to the boy. "With Abe," a brother once recalled, "it was study, study, study."

Mr. Fortas also began violin lessons as a youngster and ultimately became accomplished, playing the violin and viola in ensemble with some of the greatest living musicians: Pablo Casals, Isaac Stern and Van Cliburn. Mr. Fortas was still playing private Sunday evening concerts in his home at the time of his death.

His academic prowess won him a scholarship to Southwestern College in Tennessee at the age of 16 and then to Yale Law School, where he was editor-in-chief of the Yale Law Journal. Teaching at Yale then was William O. Douglas, a longtime friend of Mr. Fortas and, most of the time, an ideological ally on the Supreme Court.

Mr. Fortas spent the 1930s commuting between Yale, where he taught law, and Washington, where he more than held his own in the fast company of the young New Dealers who were the "brain trust" of Franklin D. Roosevelt.

By age 29, he was general counsel for the Public Works Administration. At 32 he was under secretary of the Interior for Secretary Harold Ickes, earning a reputation as a brilliant, but occasionally arrogant and sharp-tongued, intellectual. In 1943, he engaged in an angry dispute with Wayne Morse, then a member of the War Labor Board and later a U.S. senator.

Mr. Fortas wrote to him that "no one can doubt that you are completely unsuited for any position which requires the exercise of judgment and balance."

In 1935, Mr. Fortas married Carolyn Agger, a Yale law graduate who became a highly regarded corporate lawyer in the firm Mr. Fortas later formed with other alumni of the Roosevelt administration: Paul Porter and Thurman Arnold. The firm is now called Arnold & Porter.

Mr. Fortas became a rich man in that firm, representing the country's large corporations such as Lever Brothers, Coca-Cola, Pan American and Philip Morris, in what came to be called Washington's new "law industry," a buffer between business and the expanding government.

In 1948, Lyndon Johnson, then a member of Congress from Texas, sought out Mr. Fortas to represent him in a court fight stemming from the disputed primary election for the U.S. Senate. Mr. Fortas appealed to Justice Hugo L. Black, who set aside a lower court order that could have kept Johnson's name off the ballot in the general election. Johnson won the general election handily.

Johnson and Mr. Fortas became friends. "They were an unlikely team," Richard Harwood wrote years later in The Washington Post. "Johnson was a huge, earthy and sometimes vulgar man--emotional, outgoing, uninterested in cellos or Pablo Casals. Fortas, by comparison, was almost petite, the ultimate cloistered intellectual, an ascetic, secretive man who dealt with his young lawyers like a testy schoolmaster, who treasured his privacy and his music and objets d'art and the Rolls Royce."

In 1965, Arthur Goldberg left the Supreme Court to become U.S. ambassador to the United Nations. For the "Jewish seat," previously occupied by Louis D. Brandeis and Felix Frankfurter, Johnson chose Mr. Fortas.

The Senate confirmed Mr. Fortas on August 11, 1965. In his years on the bench, Mr. Fortas participated on the winning and liberal side in numerous historic rulings:

With Mr. Fortas, the court upheld the Voting Rights Act, struck down the poll tax as unconstitutional, struck down laws prohibiting interracial marriage, guaranteed (in the Miranda ruling) the right of criminal suspects to remain silent and consult a lawyer before questioning, and gave state criminal defendants the right to a speedy trial.

Mr. Fortas wrote two particularly important opinions.

In a 1967 ruling, in a case called In Re Gault, Mr. Fortas wrote the decision extending to juveniles many due process protections previously reserved only for adult defendants.

In 1969, in Tinker v. Des Moines Independent Community School District, Mr. Fortas said that high school students had the right to engage in peaceful protest in their schools, to protest the Vietnam war by wearing black armbands.

"Under our Constitution," he wrote, "free speech is not a right that is given only to be so circumscribed that it exists in principle but not in fact. Freedom of expression would not truly exist if the right could be exercised only in an area that a benevolent government has provided as a safe haven for crackpots. The Constitution says that Congress (and the states) may not abridge the right to free speech.

"The provision means what it says."

Mr. Fortas had become an extremely wealthy man before joining the court. Friends guessed in the early 1960s that his income was $250,000, an extraordinary sum at that time.

Yet his financial relationships and his close relationship with Johnson proved his undoing on the court. The justice's troubles began in June 1968 when Warren announced his intention to resign. Johnson nominated Mr. Fortas to succeed him as chief justice.

Republicans in the Senate, in the first of many fights over the next few years over Supreme Court nominations, dug up the fact that Mr. Fortas had accepted $15,000 to teach eight summer seminars at American University and used it against him at his confirmation hearing. In addition, they attacked him for refusing to discuss details of his role as an adviser to LBJ. Mr. Fortas believed it would invade executive prerogatives to divulge his conversations.

President Johnson, weakened politically by the Vietnam war, learned that there were insufficient votes to cut off a filibuster against the Fortas nomination. Mr. Fortas withdrew.

President Nixon wanted very much to put his own people on the court. On May 5, 1969, Life Magazine (with information provided in part by then-Attorney General John M. Mitchell, as it turned out) reported that while on the court, Mr. Fortas had accepted and later returned a $20,000 fee from the Wolfson foundation. Mr. Fortas denied wrongdoing, saying he had never spoken with Wolfson or anyone else about the Wolfson legal troubles.

Threats of impeachment, followed by further allegations that Mr. Fortas had been promised an annual gift of money by the foundation for the rest of his life, brought pressure from the White House on Warren to persuade Mr. Fortas to resign.

"It's just as if an automobile hit me as I stepped off the curb," Mr. Fortas told The Washington Post. "I wouldn't think the driver is a fiend or an evil man. I'm not the kind of man who looks for that kind of thing . . . . If I stayed on the court there would be this constitutional confrontation that would go on for months. Hell, I feel there wasn't any choice for a man of conscience."

Mr. Fortas never returned to his old law firm. He never resumed a high-profile life in law and government. Neither did he become a recluse, however. He accepted novel and challenging cases from major clients across the country. He devoted much energy to the Kennedy Center as a member of its board.

Members of the court mourned Mr. Fortas's death. "He was extraordinarily nice to me on every occasion when our paths crossed," said Justice Harry A. Blackmun, who took his seat.

"He made a very distinct contribution in many areas of public service," said Justices William J. Brennan Jr. and Thurgood Marshall, who served with him. "He was not only our esteemed colleague but also a close friend."

"Justice Fortas had an illustrious career as a member of the bar and of public office," said Chief Justice Warren E. Burger.

Mr. Fortas is survived by his wife, of Washington.