Former Secretary of State Cyrus R. Vance, who helped guide foreign policy through many major Cold War events of the 1970s and then resigned to protest President Jimmy Carter's use of force in an attempt to free Americans held hostage in Iran, died yesterday at Mount Sinai Medical Center in New York. He was 84.

His son, Cyrus R. Vance Jr., said he had Alzheimer's disease.

Vance and William Jennings Bryan were the only two secretaries of state to quit over principle. Bryan left over the nation's entry into World War I; Vance broke with Carter in April 1980 when the president, over Vance's vehement opposition, gave the green light for the U.S. military to try to rescue the hostages who had been held for months by Muslim militants in the U.S. Embassy compound in Tehran.

"I knew I could not honorably remain as secretary of state when I so strongly disagreed with a presidential decision that went against my judgment as to what was best for the country and hostages," Vance later explained.

Vance did not immediately announce his resignation but gave it to Carter without waiting for the outcome of the mission, which failed when a rescue helicopter and a cargo plane collided in the Iranian desert, killing eight American servicemen.

A few days later, Vance quietly walked away from the councils of the Carter administration and his position as one of the Democratic Party's most influential voices on foreign policy.

Vance was born in Clarksburg, W.Va., on March 27, 1917. He attended Yale University, where he earned both a bachelor's degree and a law degree, graduating from the law school with honors in 1942.

After World War II service as a naval gunnery officer, Vance began an association with the influential Wall Street law firm of Simpson, Thacher & Bartlett, which, except for his periods of government service, would continue throughout his life. He also became active in Democratic Party affairs.

When John F. Kennedy became president in 1961, Vance began climbing the upper ranks of the foreign policy and national security apparatus. In quick succession, he served as general counsel of the Defense Department, secretary of the Army and deputy defense secretary under President Lyndon B. Johnson.

He left government in 1967 but returned in 1968 to be Johnson's special envoy in the crisis over North Korea's seizure of the U.S. intelligence ship Pueblo and deputy chief American delegate to the Paris Peace Conference on Vietnam.

By the time Richard Nixon was elected president in November 1968, Vance was regarded as an establishment pillar.

Vance became secretary in an administration determined, sometimes haltingly and amid great controversy, to change the conduct and administration of U.S. policy. Under Vance, the State Department began a vigorous emphasis on human rights that traditional diplomats criticized but much of the Third World admired. He also began the first truly concerted effort to recruit women and minorities for leading department posts. The Carter-Vance team worked vigorously to engage the Soviet Union in a variety of arms-control initiatives.

In terms of specific foreign policy accomplishments, the first three years of the Carter administration were especially fruitful. It won congressional approval for turning the Panama Canal over to Panamanian sovereignty, the Camp David peace accords between Israel and Egypt were signed, and the U.S. decided to recognize Beijing as the sole, legitimate government of China.

In all of these initiatives, Vance was among the major players, although his quiet, self-effacing manner frequently obscured the size and importance of his role. In contrast to his predecessor as secretary, the flamboyant Henry A. Kissinger, Vance approached diplomatic negotiation with a low-key but persistent and no-nonsense attitude that one senior State Department official had characterized as "the quintessential Wall Street lawyer. Whatever the matter on the table, he saw it as a contract that wasn't quite ready for signature but that could be gotten there with just a little more work."

A man of many ascetic qualities, he had commuted in New York by subway, and on his first official trip overseas, he traveled by commercial airline. Even on Air Force transportation, Vance, usually wrapped in an old cardigan, insisted on a style of travel so minimalist that a reporter described traveling with him as "Protestant ethic tours -- the idea that if you have to go to far-off exotic places, you should do it under conditions of severe austerity that ensure you won't enjoy it."

Vance's tenure was troubled by rivalry with Zbigniew Brzezinski, Carter's national security adviser, who spoke out in provocative ways, frequently without consulting Vance. Moreover, he often took hawkish and anti-Soviet positions that ran counter to Vance's quieter efforts to seek consensus with Moscow.

Carter was forced to intervene, but the rivalry persisted, and Vance, weary of the infighting and under pressure from his wife to return to private life, confided that he intended to leave at the end of Carter's first term.

But in late 1979, the hostage crisis broke out. Pressure to win the hostages' release was enormous. Carter authorized the rescue mission at a meeting attended by Brzezinski but not Vance, who was vacationing in Florida. Vance rushed back and asked for a chance to argue against it.

At a following meeting, he insisted that the mission would anger American allies who had agreed to impose sanctions on Iran only after the administration had promised to give them a chance to work. Vance also argued that risks to the hostages and bystanders were too great. But his arguments failed.

Returning to his law practice, Vance served briefly as chairman of the Federal Reserve Bank of New York and was instrumental in brokering a series of temporary cease-fires between feuding factions.

"A champion for peace and human rights, he was a superb statesman who served me and other presidents well," Carter said in a statement from himself and his wife, Rosalynn. "We will miss his friendship, and the world will miss his humanitarian work and goodness."

Vance is survived by his wife, five children and two grandchildren.

Cyrus R. Vance, right, talks with Henry Kissinger, left, and former ambassador U. Alexis Johnson at an awards ceremony in Washington in 1980. Kissinger was Vance's predecessor as secretary of state.