Archibald Cox, 92, the Harvard law professor and special prosecutor whose refusal to accept White House limits on his investigation of the Watergate break-in and coverup helped bring about the 1974 resignation of President Richard M. Nixon, died yesterday at his home in Brooksville, Maine.

His wife, Phyllis, said last night that she could not specify a single cause of death. “He was 92 years old, and I think he died of old age,” she said.

In October 1973, Cox precipitated what would become known as the “Saturday night massacre.” He did this by insisting on unrestricted access to tape recordings of presidential conversations in the Oval Office during the period immediately after five men with links to Nixon’s Committee to Re-elect the President had been arrested in the June 1972 break-in at the Watergate headquarters of the Democratic National Committee.

An angry Nixon demanded Cox’s firing. But Attorney General Elliot Richardson, who had recruited Cox as the Watergate special prosecutor, refused to carry out the president’s order. He resigned, as did his deputy, William D. Ruckelshaus. Robert H. Bork, who as solicitor general was the third-ranking officer of the Justice Department, dismissed Cox.

Almost overnight, from Capitol Hill and in the national media, came the sounds of protest and dismay. Sen. Barry M. Goldwater (Ariz.), one of the most influential Republicans in Congress, declared that Nixon’s credibility “has reached an all-time low from which he may not be able to recover.”

In the House of Representatives, members introduced 22 bills calling for the impeachment of the president or an investigation into impeachment proceedings. More than a million telegrams demanding impeachment poured into congressional offices.

Newspaper editorial writers and columnists made somber references to an “attempted coup d’etat.” Cox appeared on the cover of Newsweek magazine, wearing his trademark bow tie, neatly knotted as always. Time had photos of Cox and the president facing each other over the caption, “Nixon on the Brink.”

The firing of Cox, on Oct. 20, 1973, came at a time of high turbulence and political unrest. The Watergate scandal was increasingly engulfing the Nixon presidency. A summer of televised hearings on Capitol Hill had produced a steady flow of testimony suggesting burglary, lies, duplicity and criminality at the highest levels.

One witness testified that Nixon routinely tape-recorded all conversations in the Oval Office. On July 9, 1973, Cox subpoenaed nine of the tapes. The White House resisted, citing the doctrine of executive privilege. Nixon proposed that Sen. John Stennis (D-Miss.) review the tapes and verify their content to the prosecutor’s office. To Cox, that was unacceptable. He wanted the raw tapes, unedited and unabridged. When he refused to back down, Nixon ordered his firing.

Cox was replaced by Leon Jaworski, who eventually got the disputed tapes, and the Watergate investigation continued. If anything, the firing of Cox increased its momentum. “The Saturday night massacre was the single event in his long and controversial political life from which Richard M. Nixon, president of the most powerful nation in the world, would never recover,” wrote Ken Gormley, a Duquesne University law professor, in “Archibald Cox: Conscience of a Nation,” a 1997 biography.

In a foreword, Elliot Richardson wrote, “Had Richard Nixon known Archie Cox . . . Nixon would have realized that his only hope of salvation lay in full disclosure.” Richardson said Nixon believed that Cox, who had been associated with President John F. Kennedy, was out to get him.

“Try as I might, I could not convince Nixon or his staff that Archie would rather cut off his right arm than take any action not fully supported by the law and the facts. . . . In the end Nixon’s most damaging misjudgment was his underestimation of Cox’s ability to communicate the strength of his integrity.”

At a Saturday afternoon news conference hours before he was fired, Cox insisted: “I’m certainly not out to get the president of the United States. . . . I decided I had to try to stick by what I thought was right.” In a formal statement after his dismissal, he said simply that “whether we shall continue to be a government of laws and not of men is now for the Congress and, ultimately, the American people to decide.”

He would later observe that “one of the important lessons of Watergate was that unless the government trusts the people and conducts itself in an honorable fashion, then the people won’t trust the government. . . . The long-range aim of the Watergate investigation and prosecution was to show that the government could cleanse itself and be put in a shape that the people could trust.”

Before Watergate, Cox served in government jobs as solicitor general during the Kennedy administration and as chief of the Wage Stabilization Board during the Truman administration. As solicitor general, he argued civil rights and reapportionment cases, and he helped persuade Chief Justice Earl Warren to head the commission that investigated the assassination of President Kennedy. He resigned in 1965 during the second full year of the Johnson presidency, telling friends he felt unwanted and unappreciated.

In 1952, during the Korean War, he resigned from the Wage Stabilization Board in protest against the president’s overruling of a board decision that lowered a wage increase negotiated by United Mine Workers chief John L. Lewis.

He was a nationally known expert in labor and constitutional law and the author of several books in these fields, including “Law and the National Labor Policy,” “The Warren Court: Constitutional Decision as an Instrument of Reform” and “The Role of the Supreme Court in American Government.” After each government assignment, he returned to Harvard, where as a professor he was known for an incisive mind and clarity of expression.

His biographer, Gormley, described him as a man of “Harvard tweeds, a sharp New England profile, brisk walk, erect posture . . . [who spoke in] sentences that could be diagramed with precision.”

He was the prototypical Proper Bostonian. On the night of Oct. 20, 1973, when formal notification of his dismissal as Watergate prosecutor arrived at his suburban Virginia home, Cox complained to family members that the messenger bearing the news should at the very least have been wearing a coat and tie.

At Harvard in the late 1960s, he had been assigned to keep order during a time of student unrest. The student newspaper, the Harvard Crimson, praised him for “finesse and strength” but called him “aloof and evasive” as an enforcer.

Archibald Cox was born in Plainfield, N.J., into a well-to-do and well-connected family.

A great-grandfather had been a U.S. senator from New York and the lawyer who defended President Andrew Johnson at his impeachment trial. One of his uncles was Maxwell Perkins, the famed editor at the Scribners book publishing house.

After graduating from Harvard, he received a law degree magna cum laude from Harvard Law School. For a year, he was law clerk to Judge Learned Hand, the celebrated U.S. appellate jurist, then joined the blue-chip Boston law firm of Ropes, Gray, Best, Coolidge & Rugg.

He first came to Washington in 1941 to serve on the National Defense Mediation Board staff. Later, during World War II, he was in the solicitor general’s office in the Justice Department, and then was an assistant to an assistant secretary of state.

He joined the Harvard Law School faculty after the war, and in 1946, at 34, was made a professor, one of the youngest at Harvard. For the next 15 years, with periodic timeouts for government jobs, he was on the Harvard faculty. In 1958 and 1959, Cox was an adviser to then-Sen. John F. Kennedy (D-Mass.) on matters involving labor legislation, and during the 1960 presidential campaign, he worked full time on Kennedy’s campaign staff. On Christmas of that year, Kennedy telephoned to ask him to be solicitor general.

Five years later, he returned once again to Harvard, teaching constitutional law, which he loved. At Harvard in the spring of 1969, hundreds of students were arrested by club-swinging police after the university called for law enforcement authorities following a takeover of University Hall. Shortly thereafter, Cox was handed responsibility for the preservation of a fragile campus order.

At 61, in May 1973, he was beginning to slow down when Richardson called to ask whether he’d take the job of special Watergate prosecutor. After Watergate, he returned yet again to teaching. He was president of Common Cause, the self-styled citizens lobby, and he argued cases before the Supreme Court from time to time. He had been living year-round in Brooksville since 1999.

When Bork, the solicitor general who had fired him as Watergate prosecutor, was nominated by President George H.W. Bush to the Supreme Court, Cox steadfastly refused to take a position on the controversial nomination. “I don’t think that a man who’s been as personally involved in the firing as I was can separate out his personal feelings from judgments on the way other people acted,” Cox said. “Those are judgments impartial people, who weren’t embroiled, should make.” Bork’s nomination was defeated.

On June 12, 1937, Cox married Phyllis Ames. They had three children, Sarah, Archibald Jr. and Phyllis.

Staff writer Martin Weil contributed to this report.