THERE is a growing feeling in Washington that while a European Commission-brokered peace may have stemmed the initial violence, Yugoslavia now faces an almost inevitable breakup in the wake of the military's clumsy attempts to hold the country together by force.This perception lies behind the Bush administration's sudden shift from cautious urging of Yugoslav unity to apparent cautious acceptance of independence for the Yugoslav republics of Slovenia and Croatia. Only a few days ago, American officials were insisting that the breakaway republics wouldn't gain US recognition. They now refuse to repeat that assertion and instead are emphasizing that the "aspirations" of Yugoslavia's various ethnic groups be honored. Though subtle, as shifts in foreign policy often are, the change is unmistakable. But as before, the United States continues to urge that, whatever happens, the Yugoslavs settle differences through negotiations, not fighting. "We support whatever the Yugoslavian people decide the Yugoslavian people want for themselves," said State Department spokeswoman Margaret Tutwiler last week. Part of the reason for the US change of heart is the opinion of some European allies. Germany, mindful of its own recent experience with national aspirations, is continuing to urge that the desires of Slovenia and Croatia not be dismissed lightly. Italy, Belgium, and, to some extent, Britain have all begun following Germany's lead. France has been less enthusiastic, pointing out that the dismantlement of Yugoslavia could unloose fractious forces in Czechoslovakia and Romania, among other Eastern European nations. Yugoslavian leaders agreed yesterday to give the Slovenian republic limited control over its international borders while a formula is worked out for Slovenia's peaceful secession. THE main reason the US has shifted its position on the Balkans is simply recognition of the way the wind is blowing. By acting so hastily to try to assert control over Slovenia, the Yugoslav military has proved that force is no solution to the country's problems. For one thing, the military now has proof the republics will fight back tenaciously if attacked. For another, it has exposed an apparent split between itself and the weak federal government, which has been distancing itself from the Army's actions. It now is clear that the only way the military can be successful is to subject Slovenia and Croatia to brutal suppression. That would be unacceptable, not only to the republics involved, but also probably to the central government, and certainly to the United States. "That would be no solution. It wouldn't solve Yugoslavia's economic problems. It would isolate and alienate Yugoslavia even more from the Western world," says F. Stephen Larrabee, an Eastern European expert at the RAND Corporation. Though ethnic hatred and nationalism lies behind much of Yugoslavia's current trouble, Mr. Larrabee and other experts say long-term economic forces are also playing an important part in the country's breakup. Virulent inflation, unemployment, and crushing foreign debt have all conspired to push Yugoslav living standards back to the level of the 1960s, exacerbating differences between regions and adding to distrust of the central authority. Slovenia, for instance, feels it could well benefit economically from independence. With only 8 percent of the country's population, this most-Westernized of Yugoslav republics produces some 20 percent of the country's gross national product. It accounts for an estimated 25 percent of hard-currency exports. Yet Slovenians feel much of their wealth is siphoned off by the central government and used to support and develop less-well-off areas - such as Serbia and Macedonia, areas that strongly favor continu ation of the Yugoslav federation. Susan Woodward, an expert on the Yugoslav economy and visiting fellow at the Brookings Institution in Washington, argues that when things other than income taxes, such as customs subsidies, are taken into account, Slovenia is not a producer of excess wealth for propping up other segments of Yugoslavia's economy. But she points out that the Serbs now believe strongly in a centralized industrial policy for national development, while Slovenia and Croatia are much more free-market oriented. Even though the two breakaway republics now have freely elected and avowed noncommunist leaders, it would be a mistake to think they are free in the Western sense, according to US experts. Franjo Tudjman, Croatia's president, was thrown out of the old Communist Party for being too nationalistic. In Croatia, "the press is now more controlled than it was under communism," says Ms. Woodward.