BRUSSELS - A proposal by George W. Bush, the Republican presidential candidate, to remove U.S. troops from peacekeeping missions in the Balkans has provoked a wave of anxiety among the European allies, who fear such a move would split the NATO alliance and damage faith in American leadership.

While reluctant to be drawn into the final stages of the U.S. election campaign, senior European diplomats and officials at NATO headquarters said Mr. Bush's call for a new division of labor within the Western alliance threatened to erode principles of shared risk and collective security that have sustained the Atlantic military partnership for more than half a century.

''If the United States says it will not perform certain tasks, then the basic consensus of 'all for one and one for all' begins to unravel,'' a top European ambassador said. ''Once you allow NATO members to pick and choose their operations, then where does it all end? The integrated military command could soon fall apart, and so would the alliance.''

Other European officials recalled how the early stages of the Bosnia conflict nearly caused a fatal rupture in the Western alliance, when the United States refused to send troops but agreed to fly air support while European peacekeepers were hunkered down on the ground. The disparity in the perils and perspectives of alliance forces prompted fierce policy arguments that NATO leaders vowed must never be repeated.

''It's a false distinction to put American forces at one end of the spectrum and Europeans at the other,'' said Simon Lunn, secretary-general of the NATO parliamentary assembly, which brings together legislators from the 19 members. ''It challenges the essence of collective security that lies at the heart of the alliance and all of its military operations.''

The alarmist sentiments voiced by European diplomats and NATO officials were triggered by comments from Mr. Bush's senior national security adviser, Condoleezza Rice, who told The New York Times that the United States should now focus on fighting or deterring wars in the Gulf and Asia while turning peacekeeping duties over to European countries.

''The governor is talking about a new division of labor,'' Ms. Rice was quoted as saying. ''The United States is the only power that can handle a showdown in the Gulf, mount the kind of force that is needed to protect Saudi Arabia and deter a crisis in the Taiwan Strait. And extended peacekeeping detracts from our readiness for these kinds of missions.''

She went on to say that Mr. Bush believed performing such tasks in the Balkans had harmed the morale and combat readiness of U.S. troops.

''Carrying out civil administration and police functions is simply going to degrade the American capability to do the things America has to do,'' she said. ''We don't need to have the 82d Airborne escorting kids to kindergarten.''

In European capitals, there was almost universal criticism of Mr. Bush's proposal and consternation that it could inflict a mortal blow to the NATO alliance.

Even the conservative Times of London warned that splitting military tasks within the alliance in ways that curtailed U.S. participation in conflict management and peace-building was a reckless enterprise.

''Most troublingly, the Bush plan for a 'division of labor' in NATO would in effect decouple the U.S. from the defense of the European continent - a huge strategic shift, and a dangerous one,'' the English newspaper said in its lead editorial.

NATO military officers contended that missions to promote stability in a future European order would undoubtedly involve security tasks, like those now being carried out by NATO forces in the Balkans, that depart from textbook warfare. They said it would defeat the purpose of the alliance's integrated military command to reserve U.S. troops only for special kinds of combat.

''The lesson of the post-Cold War era is that armies must be highly versatile,'' said a European commander at NATO military headquarters near Mons, in southern Belgium. ''In Bosnia and Kosovo, it's true we are doing a lot of things best handled by policemen or engineers. But those tasks still help promote peace and they will be needed in future hot spots as well.''

European allies have grown exasperated lately by U.S. claims that they are not pulling their weight within the alliance. Several officials cited Mr. Bush's assertion, during a televised debate with his Democratic opponent, Al Gore, that ''one of our priorities with our European friends should be to convince them to put troops on the ground'' in the Balkans.

In fact, European troops now account for more than 80 percent of the 65,000 NATO forces deployed in the Balkans. The United States currently maintains 11,400 soldiers with the NATO-led contingents in Bosnia and Kosovo. European Union leaders also are putting finishing touches on plans for a 60,000-strong rapid reaction force capable of being deployed within one month and sustained for one year. The EU force would be dispatched to stabilize conflict zones where NATO and U.S. forces refused to become involved.