While Washington still favors a plan that gives the Muslim-controlled Bosnian Government 51 percent of the territory, the new proposal would give the Serbs the last remaining eastern Government enclave, Gorazde, in exchange for more valuable territory around Sarajevo.

To entice the warring parties to settle, the plan would lift economic sanctions against the Bosnian Serbs and promise a "mini-Marshall plan" of post-war economic aid to the Bosnian Muslims, an American official said. The United States and other Western nations would also help the Government build a military strong enough to defend its new borders.

If the deal falls through and the allies blame the Serbs, the plan calls for lifting the arms embargo against the Bosnian Government and launching air strikes against Serbian targets. If the Muslims are blamed for any failure, the United Nations peacekeeping forces would withdraw and leave the Muslims to their own devices.

If the new American peace effort succeeds, several thousand United States troops would be committed to a heavily armed NATO force to guarantee the plan, Administration officials said.

This planning has been in place for nearly two years, but until recently has not been much of an issue. But Croatia's successful military offensive against the Serbs and a split within the leadership of the Bosnian Serbs has presented an opportunity for a diplomatic settlement and forced the Pentagon to refine details on how to enforce it.

There are still several hurdles to clear before peace breaks out in the Balkans. Some Administration officials voiced skepticism that any deal was imminent. The European allies have to agree on the details. More important, the Serbs and Muslims must concur, which is far from certain.

"It has to be pursued in number of capitals," a senior Administration official said.

But if a durable peace is negotiated and Congress agrees to send troops, American forces would join a large NATO force to monitor Bosnian borders. Until the recent Croatian military offensive, NATO planners had estimated it would take as many as 35,000 NATO troops -- half of them American -- to enforce a Bosnia peace plan.