SAN JOSE, COSTA RICA, AUG. 22 -- The latest session of peace talks between the Salvadoran government and leftist rebels ended in deadlock today, with each side accusing the other of blocking the dialogue.

The lack of progress in the fourth round of United Nations-mediated talks raised the possibility of an escalation of fighting in the coming months, according to participants on both sides.

"As long as the government maintains its intransigence over {restructuring} the armed forces, a resurgence of military action is almost inevitable," said Salvador Samayoa, a negotiator for the Farabundo Marti National Liberation Front.

Neither side moved to end the monthly contacts, however, which are to continue here in September. Both sides expressed confidence that the 11-year civil war would eventually be resolved at the negotiating table.

U.N. mediator Alvaro de Soto said the meetings "have permitted us to gather some elements that could, in due course, serve to assemble substantial agreements."

The latest six-day meeting concentrated on the thorny issue of the future of the U.S.-backed Salvadoran army, on which attitudes apparently have hardened.

An 18-point rebel plan called for the eventual dissolution of the army and of the rebel forces, for the government to take the first steps toward replacing the security forces with a civilian police force, for punishment of those responsible for six prominent cases of human rights violations and for replacement of all colonels and generals. All of this would precede a truce.

"This is a new position," said Oscar Santamaria, head of the government's delegation. "It is a setback."

The rebels in turn accused the government of failing to make any concessions over the armed forces. The government maintains that the military, which faces multiplying charges of corruption and abuses of human rights, can reform itself as an institution and that a purge of officers is not acceptable.

"We are talking different languages," said the rebel Samayoa.

Last month the two sides sidestepped the military issue to sign an accord on human rights. But after criticism within rebel ranks, the leftist negotiators rejected a similar move this time. They said they fear minor agreements will tie them to a cease-fire without addressing the main problem of the army.

The rebels say the military high command is isolated and vulnerable, facing pressure internationally over the killings in November of six Jesuit priests and two Salvadoran women by members of an elite army unit. The U.S. Congress is due to vote next month on proposals to cut military aid by as much as 50 percent.

There are signs of anger among more junior officers because of the damage being done by the Jesuit case, although it is not clear whether this amounts to a serious split in the army.

The rebels, who for months have been warning they are ready to launch a new offensive, contend that they have the military initiative and that this is not being reflected at the negotiating table.

For the first time in the war, military and rebel sources say, the guerrillas have significant numbers of antiaircraft missiles. U.S. officials accuse Cuba of supplying upgraded weapons. The rebels say the missiles are easily available on the black market and that one of their sources has been the U.S.-backed Nicaraguan contras, now disbanded.

Senior military commanders appear confident that they saw the worst the rebels could do last November, when the guerrillas occupied large areas of San Salvador and other major cities for almost a week.