Samuel Dash, 79, the chief counsel of the Senate Watergate Committee whose televised interrogation into the secret audiotaping system at the White House ultimately led to President Richard M. Nixon’s resignation, died of multiple organ failure May 29 at Washington Hospital Center.

Mr. Dash spent months doggedly questioning Nixon administration officials before White House aide Alexander Butterfield testified in July 1973 that there was an extensive taping system that captured executive office discussions about the break-in at the Democratic national headquarters. Mr. Dash asked him who knew about it. Butterfield replied: “The president . . .” Nixon resigned a year later.

Mr. Dash’s 53-year legal career touched some of the most important moments in American, and sometimes world, politics. He dramatically resigned in 1998 after four years as the ethics counselor to independent prosecutor Kenneth W. Starr, charging that Starr became an “aggressive advocate” of impeaching President Clinton. He said Starr exceeded the independent counsel’s mandate, which was part of a statute that he helped draft.

As the first American allowed to interview the imprisoned Nelson Mandela, Mr. Dash wrote a magazine article about him and mediated discussions that helped free the future president of South Africa. He wrote a book that influenced Supreme Court decisions on electronic surveillance, and he advised governments on investigations into human rights cases in Northern Ireland, Puerto Rico and Chile.

But Mr. Dash probably will always be associated with the investigation that led to Nixon’s resignation.

Mr. Dash was offered the Watergate committee job by Sen. Sam Ervin (D-N.C.), who promised him independence and the ability to hire his own staff. He became so well known as a result of the televised Watergate hearings that he often was mistaken for a senator, and he said he could not buy socks without clerks asking for his autograph. Opponents came to describe him as a prima donna.

It took months after Butterfield’s revelation to get the Nixon tapes released, but it wasn’t until 1981 that Mr. Dash dropped by the National Archives to listen to them.

“I didn’t want to go over there just by myself,” Mr. Dash told a Washington Post reporter. But when Georgetown University faculty colleagues went to listen to the tapes, he went along and said he was glad he had. “There’s quite a difference between reading the cold print in the transcripts and actually hearing the voices and intonation -- the conspiratorial tone of voice.”

It was a point of pride for Mr. Dash that, as a result of Watergate, all accredited law schools require a course in professional responsibility.

In the 1970s, he helped Chief Justice Warren E. Burger devise the American Bar Association’s ethical standards for prosecutors and criminal defense lawyers.

While on the Starr commission, he helped persuade White House intern Monica Lewinsky to testify. But his relationship with Starr was thorny; Mr. Dash’s liberal supporters had been shocked when he agreed to take on the job, and he threatened to quit five times before he finally did on Nov. 20, 1998.

It was his timing and style as much as the fact of his resignation that was dramatic; it came the day after Starr testified for 12 hours before the House Judiciary Committee, and it came in a stinging two-page letter that charged Starr with “abuse of your office” for exceeding his mandate to report to Congress any impeachable offenses he had discovered.

Mr. Dash cultivated a reputation for independence and was an advocate for legal ethics throughout his career. In 1951, while a teaching fellow at Northwestern University near Chicago, he conducted an undercover investigation into corruption at the Municipal Court of Chicago that resulted in a seminal report on legal corruption.

For the International League for Human Rights, he investigated the killings of Northern Ireland Catholic youths by British paratroopers in 1972, during what became known as “Bloody Sunday,” and published a report that helped influence the British parliament to award compensation to the families of the dead and wounded. Twenty-five years later, the report helped influence the British prime minister’s decision to reopen the inquiry.

During the 1980s, Mr. Dash investigated the killing of students in Puerto Rico by government agents. He also served as a mediator in Chile during an appeal by human rights leaders who had been exiled from Chile by a court. That country’s supreme court reversed the exile order.

Mr. Dash joined the Philadelphia district attorney’s office in 1952 and was appointed district attorney in 1955 at age 30. He went into private practice the next year and conducted a nationwide investigation of wiretapping, resulting in a 1959 book, “The Eavesdroppers,” that is credited with helping change the Supreme Court’s position and federal and state laws on electronic surveillance.

One of his daughters, Judi Dash, said yesterday that her father, who had been in Washington Hospital Center since January because of declining health, had been able to see a copy of his next book, “The Intruders: Unreasonable Searches and Seizures from King John to John Ashcroft,” which will be published in June.

“It deals with the violations of individual rights and the Patriot Act,” she said. He was being wheeled from dialysis to his room as they discussed President Bush’s State of the Union speech in which he urged continuation of the Patriot Act. “He then lectured the orderlies on the dangerousness of the Patriot Act,” she said. While in the hospital, he planned another book, to be called “The Interrogators,” on the rights of witnesses, she said.

In 2002, Mr. Dash served on a task force to reform the ethical standards and organization of the United Way of the National Capital Area.

Mr. Dash, who was born in Camden, N.J., enlisted in the Army Air Forces during World War II and flew reconnaissance over Italy. After the war, he graduated with a bachelor’s degree from Temple University and a law degree from Harvard Law School in 1950.

He was a trial attorney in the Justice Department in 1951 and then went to Philadelphia. After several years in private practice, he joined Georgetown’s law school in 1965 as a professor and as director of its Institute for Criminal Law and Procedures. He taught criminal law for nearly 40 years and last year was voted co-winner of the law school’s top teaching award.

Mr. Dash told D.C. Bar magazine in 1998 that he wanted his students to be proud of their profession. “And above all, be honest and just with themselves and have integrity. Learn to say no in situations where saying no can be difficult, where it could mean getting fired. Say no anyway, because it could lead you to greater opportunities.”

Survivors include his wife of 57 years, Sara Dash of Chevy Chase; and two daughters, Judi Dash of Beachwood, Ohio, and Rachel Dash of Charleston, W.Va.