SAN JOSE, Costa Rica (AP) _ Peace talks in El Salvador's decade-long civil war foundered Saturday over rebel demands that the government pare down its military force and purge some right-wing officers.

Little progress has been reported since the two sides reopened talks on Friday. The current round of talks are scheduled to end Tuesday.

Leftist rebels said the conservative government of President Alfredo Cristiani had so far failed to satisfy their demands for major reforms of the military.

U.N. mediator Alvaro DeSoto said he still hopes that this round of talks could still result in agreements on some political issues.

''We're waiting to see how the negotiations pan out,'' DeSoto told a news conference.

But he cautioned that no action can be expected on the political topics unless the key issue of the military is settled.

''We have been working on the subject of the armed forces, but there will be no advances unless accords are reached in that regard,'' he said.

Representatives of the guerrilla Farabundo Marti National Liberation Front, or FMLN, insist that the military should be reduced in size and purged of right-wing officers responsible for human rights violations. The rebels also want a say in the appointment of the defense minister and commander-in-chief.

FMLN representative Miguel Saenz said the latest government proposal did not go far enough.

''The government has made us a counter proposal, but we feel it doesn't satisfy our aspirations, because it only covers secondary themes,'' Saenz said.

This is the third round of negotiations since Cristiani's rightist government took office in June 1988.

In El Salvador, Cristiani indicated he rejected some of the guerrilla demands because they challenged the existence of the armed forces and could be considered unconstitutional.

''We can speak of their (the armed forces') qualitative and quantitative structure,'' Cristiani said, ''But their existence is not on the negotiating table.

''We cannot get away from our laws, especially our fundamental law which is the Constitution of the Republic,'' he added.

Cristiani spoke briefly with reporters after opening a sports event in San Salvador, the capital.

The Salvadoran armed forces, with about 54,000 members, is the second largest in Central America. Nicaragua has the largest armed forces, but the new U.S.-backed government in Managua has announced it plans to cut the size of the military as part of a peace agreement to end that country's civil war.

The current Salvadoran talks are being held under the threat of a new guerrilla offensive, if no progress is made.

The United States has been supporting a succession of governments during the decade-old Salvadoran civil war in which more than 72,000 people have been killed.

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