In Senate debates and media interviews over the years, John F. Kerry has repeatedly returned to three axioms on the use of military force: Win as much allied support as possible before going to war, listen to advice from the professionals, and, most significant, heed the many lessons of the Vietnam War.

NATO and the United Nations appear to be touchstones for the Democratic nominee, not just the troublesome hurdles that they appear to be to President Bush. In speeches over the years, Kerry repeatedly has denounced unilateral action.

Kerry's belief in working with allies runs so deep that he has maintained that the loss of American life can be better justified if it occurs in the course of a mission with international support. In 1994, discussing the possibility of U.S. troops being killed in Bosnia, he said, "If you mean dying in the course of the United Nations effort, yes, it is worth that. If you mean dying American troops unilaterally going in with some false presumption that we can affect the outcome, the answer is unequivocally no."

A more recent theme for the senator from Massachusetts has been the importance of listening carefully to military advice. It is a subject he touched on in the past but seems to have emphasized more in the current campaign as he discusses the stormy relationship the Bush administration has had with the Army, particularly with Gen. Eric K. Shinseki, who was that service's chief of staff until last year.

Kerry says his Pentagon would be more respectful of the views of his generals than Bush's has been. In August he told Stars and Stripes, the military newspaper, that he would "have it a prerequisite that the secretary of defense work effectively with the professional military, listens to their advice, and . . . is respectful in the way we do disagree with it." The Bush administration's handling of the top brass, he said, has had "a chilling effect" on military advice -- a charge seconded by some top officers at the Pentagon.

But the most significant factor in shaping Kerry's views on the use of force appears to be Vietnam -- and not just the lesson that the conflict was a mistake. Indeed, some of his conclusions about the war are surprising, such as his praise a decade ago for President Richard M. Nixon's 1972 "Christmas bombing," the most intense aerial campaign of the war.

Kerry's reading of that war's lessons also leads, unexpectedly, to a similarity with Bush: an inclination to persist once he has chosen a course of action. His bottom line on Vietnam is that the nation must stick to commitments once troops have been sent in. The lesson from that war, he told author Gil Dorland, is that "I won't put American soldiers in harm's way unless the United States is prepared to win."

As the future of Iraq has emerged as a critical political issue, the Bush campaign has attempted to paint Kerry as both indecisive and so negative about the U.S. presence there that he would never achieve success. The reality of Kerry's record is more complex. More often than not, he has backed the use of force, especially after diplomacy has been tried extensively.

He opposed U.S. support for right-wing "contra" forces in Nicaragua in the 1980s but supported military action in Panama in 1989. He voted against going to war against Iraq in 1991 but supported military action in Haiti and the Balkans and voted to authorize war against Iraq in 2002. In many of these cases, he argued for international operations, involving the United Nations or NATO, but, in the case of the 2002 debate over Iraq, he was willing to authorize war without guarantee of broad allied support.

Likewise, he has a mixed record on key weapons programs, supporting most defense bills but opposing some that funded systems such as the B-2 stealth bomber, which he called too costly.

"There's no question he's wandered around" on issues such as the use of force, but so have most senators, said a Republican colleague and friend who supports Bush but also admires Kerry. "I don't think he would hesitate to use force if U.S. interests were threatened," he added.

"He doesn't shy away from defending America's interests . . . but he believes it is important to get international support," said Sen. Carl M. Levin (Mich.), ranking Democrat on the Armed Services Committee.

Conservatives argue that Kerry's emphasis on multilateralism would result in weak coalitions unable to further U.S. interests.

"What it means, practically, is that you always go to the lowest common denominator," said Tom Donnelly, a defense expert at the American Enterprise Institute, "so whatever the least willing member of the coalition is willing to do, that defines the policy."

Staff researcher Lucy Shackelford contributed to this report.