OAXTEPEC, MEXICO, JUNE 25 -- Negotiators for the Salvadoran government and leftist guerrillas completed a week of talks here today with no agreement toward ending their decade-old civil war, but a U.N. mediator and rebel spokesmen said the negotiations had marked important progress.

The talks in this resort town 50 miles south of Mexico City ended as a U.S. congressional committee prepares to vote this week on a proposal to reduce U.S. military aid to El Salvador sharply. Aid currently is running at more than $85 million a year.

The negotiations were the first in which the two sides have had substantive conversations about what most analysts agree is the most difficult obstacle to ending a war that has left more than 72,000 people dead -- reforming El Salvador's armed forces.

"There still haven't been agreements," U.N. mediator Alvaro de Soto said today. "However, there is a clear commitment to reach agreements in the timetable agreed to in Caracas, and there has been movement in this direction that has no precedent in the history of contacts between the government" and the rebel Farabundo Marti National Liberation Front (FMLN).

In talks last month in Caracas, Venezuela, the two sides set goals for a cease-fire in September and an end to the war in March 1991.

The rebels have demanded measures that would reduce the size and role of the 55,000-man armed forces and eliminate or restructure the country's paramilitary civil patrols and the security forces, which include the treasury police, the national guard and the national police.

Although government negotiators were not available for comment at the conclusion of the talks, it did not appear that they made any important concessions on those demands in the current round of talks. However, de Soto said the two sides had been able to "identify and make progress" on issues related to the armed forces.

Rebel spokesmen agreed that the talks marked progress toward a cease-fire and final resolution of the war, but the FMLN has said it will not agree to a cease-fire before an agreement is reached on the armed forces, which human-rights groups consider to be largely autonomous and responsible for most civilian deaths in the war.

Among a number of demands, the rebels are asking for prosecution of army officers believed responsible for the murders of Archbishop Oscar Arnulfo Romero in 1980 and six prominent Jesuit intellectuals at the University of Central America at the height of a major guerrilla offensive in San Salvador last November.