BUDAPEST -- The United States and Russia paved the way for an agreement Monday that would send a multinational peacekeeping force into Nagorno-Karabakh, one of the former Soviet Union's worst troublespots.


A senior U.S. official indicated to reporters that disagreements with Russia over the operation in principle had been ironed out -- though details of the make-up of the 3,000-strong force had still to be tackled.


The official, who did not wish to be identified, said the two powers hoped the 53-nation Conference on Security and Cooperation in Europe (CSCE), meeting in Budapest, would approve the operation.


"What we have achieved now ... is agreement by the Russians, and hopefully by everybody else, that the CSCE, working with the Russians, should be the central focus of the peace process," he said.


Russia, the regional big power closest to the fighting in Trancaucasia, has been pressing for control of the operation and for the right to provide the bulk of the force.


But one CSCE delegation member said it had been agreed that no single country would be able to contribute more than 30 percent of the force.


"It's looking good and it will be signed tomorrow," this official said.


CSCE officials have put the cost of the operation, which will commit the multinational force to harsh mountainous conditions, at around $40 million for the first six months.


Earlier U.S. President Bill Clinton, in a speech at the opening session of the CSCE summit, said: "We are on the verge of an agreement."


It will be the first time the CSCE has initiated a peacekeeping operation and falls in line with plans to give the organization, until now little more than a talking shop, a real role on a continent beset by conflicts.


Agreement had been held up earlier by Russian demands for a free hand in the mission on the grounds it has a special interest in managing conflicts left over from Soviet days on its southern rim.


Thousands have died in Nagorno-Karabakh -- largely populated by Armenians, although it is in Azerbaijan -- since the conflict broke out in 1988 when the territory sought to break away.


Karabakh Armenian forces, enjoying logistical and some manpower support from Armenia, have firm control of Karabakh as well as occupying large swathes of Azerbaijani territory.


The U.S. official, asked about U.S. Secretary of State Warren Christopher's comment Sunday that the Russians would have "something less than 50 percent" of the force, said details of its make-up and its command structure would be decided later.


The official said an uneasy truce, which has been holding in the territory since May, would have to become a formal cease-fire, after which the peacekeepers could be sent in.


This could be then followed by a convening of the 11-nation so-called Minsk group of the CSCE to tackle a political settlement.