Cyrus R. Vance, who resigned as President Carter's secretary of state over an ill-fated attempt to save American hostages from Iran, has died. He was 84.

Vance died at Mount Sinai Medical Center after a long battle with Alzheimer's disease, said his son, Cyrus R. Vance Jr. He said he did not know the cause of death.

Heading the State Department was the highlight of Vance's career, but his duties on behalf of presidents, the Congress and the United Nations spanned more than three decades. He used his peacemaking skills to ease conflicts in foreign lands, racially torn American cities and even corporate boardrooms.

Quiet and self-effacing, Vance was a study in contrasts with Henry Kissinger, his flamboyant predecessor at the State Department. Vance's politics were far more liberal than Kissinger's, and his political leanings often put him at odds with Carter's national security adviser, Zbigniew Brzezinski.

Vance enjoyed several successes during his early period as secretary of state but suffered setbacks later on. He played a key role in normalizing relations with China, winning approval for new Panama Canal treaties and helping negotiate a peace treaty between Egypt and Israel.

But Vance's tenure also saw an expansion of Soviet influence in a number of areas as well as the collapse of the pro-American monarchy in Iran and the seizure of American hostages in Tehran.

When Carter approved a military operation for the rescue of the hostages in April 1980, Vance resigned because he felt he could not support such a plan. His skepticism proved prescient; the operation ended in disaster.

One of his most difficult diplomatic undertakings took place long after he left the State Department, when U.N. Secretary General Javier Perez de Cuellar asked him in 1991 to try to end the fratricidal war in the former Yugoslavia. He helped achieve a cease fire in Croatia but peace eluded him in Bosnia.

His strategy in Bosnia was the subject of considerable controversy. Vance felt strongly that negotiations were the only way to halt Serbian advances, rejecting critics who argued that his tactics amounted to appeasement of an aggressor.

He quit in despair after struggling with the Bosnian conflict for almost a year.

It wasn't long before he plunged into an entirely different kind of peacemaking: resolving rival creditor claims involving a debt-ridden commercial real estate firm with extensive holdings in New York City. Vance helped the parties reach a settlement in July 1993.

Cyrus Roberts Vance was born in Clarksburg, W. Va., on March 27, 1917. After graduating with honors from Yale Law School in 1942, he entered the U.S. Navy, serving as a gunnery officer in the Pacific during World War II.

A year after his discharge from the Navy in 1946, he married Grace Elsie Sloane, of a prominent family specializing in home furnishings. He joined the New York law firm of Simpson, Thatcher and Bartlett, with which he maintained a relationship for decades.

In 1975, Vance and social scientist Daniel Yankelovich founded Public Agenda, a nonpartisan, nonprofit public opinion research and citizen education organization based in New York City.