Dean Rusk, 85, the former secretary of state who presided with a calm and courtly demeanor over U.S. foreign policy during a period of intense division and bitter controversy about U.S. involvement in the war in Vietnam, died of congestive heart failure Tuesday at his home in Athens, Ga.

Rusk was secretary of state for Presidents Kennedy and Johnson from 1961 to 1969, a period that included the ill-fated Bay of Pigs invasion of Cuba, the Cuban Missile Crisis and the signing of the nuclear nonproliferation treaty with the Soviet Union. Only Cordell Hull, President Franklin D. Roosevelt's secretary of state, served longer in that office.

Rusk, a mild-mannered and self-effacing southerner, became a focal point for the scorn and vitriol of antiwar street demonstrators and other opponents of the war in Vietnam as U.S. involvement in the conflict escalated. But he remained outwardly unperturbed and aloof from the tempest, and he stuck to his conviction that a secretary of state's responsibility was to supply facts and information to the president, not to answer criticism or engage in political debate.

Only after leaving office did Rusk indicate any second thoughts about the Vietnam policy he had advocated.

"It was a mistake to enter and fail," he told a House committee at a hearing on U.S. involvement in the war six years after leaving office. He acknowledged in a 1973 interview with The Washington Post that "I underestimated the tenacity of the North Vietnamese, and I overestimated the patience of the American people."

His greatest achievement as secretary of state, he said, was having helped add eight years to the period in history in which no nuclear weapons were fired in anger. The media often called him "inscrutable" or "Sphinx-like," descriptions compatible with his own view that the office should be "depersonalized."

A Rhodes scholar who served as an aide to Gen. Joseph W. "Vinegar Joe" Stilwell in the China-Burma-India theater during World War II, Rusk joined the State Department after the war. He embraced the principle that communist aggression should be contained and that force should be met with force. He carried that conviction throughout his public career.

"If the communist world finds out we will not pursue our commitments, I don't know where they will stay their hand," he once told Johnson.

He had been president of the Rockefeller Foundation for eight years when Kennedy picked him to head the State Department. But his low-key style and low visibility did not blend with the activism of other top figures in the Kennedy administration, and he never fit in with the bright young men the president had summoned to Washington from academia and the boardrooms of industry.

"He was a modest man in an administration not known for its modesty," observed David Halberstam in his book "The Best and the Brightest."

Arthur Schlesinger Jr., one of Kennedy's key advisers, complained that Rusk edited out all the best phrases in the drafts of presidential speeches that were sent over to the State Department for comment. Several high-ranking aides said it was unlikely that Rusk would have continued to serve as secretary had there been a second Kennedy administration.

But he found a kindred spirit in Johnson, who assumed the presidency upon Kennedy's assassination on Nov. 22, 1963. Both were southerners, both grew up poor and both were ambitious. Moreover, Rusk, along with presidential aide Walt Rostow, was the strongest supporter of Johnson's hard-line policy in Vietnam.

Rusk was born Feb. 9, 1909, on a farm in Cherokee County, Ga., the third and youngest son among five children. The family moved to Atlanta when he was 3. His father, a Presbyterian clergyman who lost his voice because of a throat ailment, spent most of his life as a mailman.

His parents taught him to value education and religion and to play strictly by the rules. He was so punctilious that, when asked years later on government security forms whether any of his family ever had tried to overthrow the U.S. government, he listed his grandfathers, who had fought in the Confederate army in the Civil War.

Rusk graduated from Davidson College in North Carolina. After three years of study as a Rhodes scholar at Oxford University in England, he joined the faculty of Mills College in California. He taught political science, married one of his students, Virginia Foisie, and rose to become dean of the faculty. In 1940, a year before Pearl Harbor, the Army called him to active duty from the Reserve.

When the United States entered the war, he was sent to the China-Burma-India theater to serve on Stilwell's staff. His cables back to Washington were clear and incisive, and when it came time to assemble a cadre of officers in Washington to begin planning for the postwar era, Rusk's name was on the list. He was ordered to Washington shortly before V-E Day.

When Gen. George C. Marshall, the Army chief of staff during the war, became secretary of state, he asked Rusk to accompany him to the State Department. Rusk's star continued to rise after Dean Acheson became secretary in 1949. By 1950, he had risen to deputy undersecretary, the third-ranking post in the department.

Rusk requested a demotion to become assistant secretary for the Far East, known then as the hottest job in the State Department, telling Acheson only that "I fit it."

The Chinese communists already had driven Chiang Kai-shek off the mainland by the time Rusk took the job, and he was in it only a few months when the North Korean army crossed the 38th parallel on June 25, 1950, and invaded South Korea. Rusk recommended that the United States intervene under the auspices of the United Nations. That became the basis for President Truman's order committing U.S. forces to battle. The U.S. action in opposing communist aggression in Korea, in Rusk's opinion, would become a model for similar action in Vietnam more than a decade later.

In 1952, Rusk accepted the presidency of the Rockefeller Foundation and began eight quiet years in Scarsdale, N.Y. When Kennedy was elected president in 1960, he was touted as a potential secretary of state by Acheson and Robert A. Lovett, a New York investment banker who was a board member of the Rockefeller Foundation and a former undersecretary of state and secretary of defense. Lovett himself was under consideration, but he declined because of his health, and others were ruled out for a variety of reasons.

Rusk had written an article in the journal Foreign Affairs in which he argued that the United States could chart its own course in foreign policy. That caught Kennedy's attention, and he offered Rusk the State Department after one meeting.

In the spring of 1961, the administration faced a decision of whether to support an invasion of Cuba by a band of Cuban exiles opposed to the regime of Fidel Castro.

"I served President Kennedy badly," Rusk wrote in a 1988 report, "Reflections on the Bay of Pigs." By confining himself to matters strictly within the jurisdiction of the State Department, he said, he failed to ask obvious and critical questions about the military adequacy of the effort, which was crushed quickly by Castro's forces.

During the Cuban Missile Crisis of 1962, Rusk urged that the United States make a public announcement about the existence of the missiles, then prepare for a strike against them while notifying the Soviets that an extremely serious crisis had developed. The crisis eventually was resolved along those lines.

On the issue of Vietnam, Rusk was unequivocal in supporting increased U.S. military pressure until North Vietnam pulled back or agreed to negotiate. He argued his case regularly at background briefings with reporters, who were not permitted under ground rules of the meetings to quote him by name. At the same time, he backed Johnson in ordering a series of bombing halts in 1968 that led to the beginning of peace talks in Paris with North Vietnam.

It was not until four years after Rusk left office that peace accords were signed. Two years later, in 1975, the United States was driven from South Vietnam.

Rusk's career in Washington ended on Jan. 20, 1969, when Richard M. Nixon succeeded Johnson as president. He went home then and taught international law at the University of Georgia.

Survivors include his wife, Virginia Rusk of Athens; three children, David Patrick Rusk of Washington, Richard Geary Rusk of Bishop, Ga., and Peggy Smith of Stafford, Va.; and six grandchildren.