WASHINGTON — A last minute Democratic hate crimes amendment on legislation to authorize a 2008 defense budget that mandates soldier pay raises and more health benefits to wounded soldiers will imperil the bill’s passage, according to Republican lawmakers and Bush administration officials.

Sixty senators voted yesterday in favor of an amendment from Senator Kennedy, a Democrat of Massachusetts, that enhances penalties for crimes against homosexuals and would be attached to the Senate bill authorizing the defense budget for 2008. The budget appropriation, which until yesterday was expected to sail through conference and be signed by President Bush, is likely to be scuttled by the provision, lawmakers say.

In the debate leading up to the vote on the Kennedy amendment, the Senate minority leader, Mitch McConnell of Kentucky, warned that the amendment could sink the bill.

“This Senate has been on record all year that we will not cut off funding for our forces in the field, and that we need to do more to help our wounded warriors returning from the war,” he said. “Let us not sacrifice the bipartisan work of the committee for an amendment that is not relevant to the underlying bill. I would hope the Kennedy amendment would be defeated.”

Senator Graham, a Republican of South Carolina, said, “The president is not going to agree to this social legislation on the defense authorization bill.”

The Senate’s defense authorization technically does not fund the wars in Iraq and Afghanistan. But many of the specific modifications to next year’s war budgets, such as those raising military pay and adding health benefits for wounded soldiers, would likely not make it into a continuing budget resolution — stopgap legislation that funds government agencies until a full budget is passed — if the Kennedy amendment torpedoes the bill that is sent to the White House.

Yesterday, the Senate majority leader, Harry Reid of Nevada, said he was proud the Senate passed the amendment, which is officially named for Matthew Shepard, a gay Wyoming college student who was murdered in 1998.

“Today the Senate sends a clear message that crimes motivated by hate will not be tolerated in America, and that such offenses will be prosecuted with vigor,” he said. “As a nation dedicated to the ideals of equality and mutual understanding, we have a special responsibility to combat bigotry that takes the form of violence.”

The move to attach the Kennedy amendment to the defense authorization bill took some Republican staffers by surprise. “The Democrats wanted a win for their base after losing all the votes on Iraq,” one Republican staffer, who requested anonymity, told The New York Sun.

The White House yesterday played its cards close to the vest. A White House spokeswoman, Dana Perino, said the president did not support the measure because local and state law enforcement has its own measures to prosecute crimes against homosexuals. She did not say specifically, however, whether Mr. Bush would veto the defense authorization bill.

On May 3, the White House Office of Management and Budget issued a threat to veto a standalone version of the Kennedy amendment that had passed the House. The statement of administration policy at the time read: “There has been no persuasive demonstration of any need to federalize such a potentially large range of violent crime enforcement, and doing so is inconsistent with the proper allocation of criminal enforcement responsibilities between the different levels of government.”