Despite mounting international pressure for a negotiated end to the Salvadoran civil war, the United States and the government it backs here continue to insist that elections are the only acceptable political solution to the conflict.

Several days of interviews here indicate, however, that there is almost no likelihood the left will participate and even less that the guerrillas will lay down their arms after the polling.

The Army, in the view of most observers here, will remain the ultimate political power in the country, although less involved in day-to-day public administration, and the steady rightward drift of the U.S.-backed government may be greatly accelerated.

There is a common expectation here that despite the rampant violence, elections for a constituent assembly will take place next March, even if most campaigning has to be done on radio, television and in the newspapers for security reasons and the state of siege, now in effect for more than a year, is only partially lifted.

But the key question remains what the elections will resolve.

Their purpose, as described by U.S. Ambassador Deane R. Hinton in a recent interview, is to discredit and isolate the Marxist-led insurgents.

"The elections will indicate very clearly that the vast majority of the people of this country are in favor of something different than these five or ten or fifteen thousand misguided individuals that are trying to destroy the country," said Hinton. "Once it becomes clear that these people who are on this destructive course are without support, then it is a question of time. The ultimate outcome is perfectly clear. How are they going to go around the world saying they represent the people of El Salvador if the people of El Salvador are on record as supporting somebody else? They don't represent anybody except themselves."

Replacement of the current military-civilian coalition government, which came to power in a coup in October 1979, with an elected civilian government, is also expected to open up new sources and quantities of desperately needed economic and military aid for the fight against the insurgents.

"The more a government is legitimized," said one prominent Christian Democratic politician, "the more possibilities it has of aid."

Ever since the United States adopted the policy in late 1979 of trying to back a centrist government in El Salvador, the government it supports here has moved steadily to the right. By all current indications, the present electoral process will accelerate that movement.

Negotiations with the left for a place in the government have been rejected out of hand by the United States and the current junta since early this year, partly because of evidence found in captured documents that the guerrillas were using negotiations as a stalling tactic until they could strengthen their military position and partly because the left's demand for a restructuring of the armed forces is unacceptable to the powerful high command.

But conservative businessmen and politicians previously shunned by the current government -- and responsible for several attempted coups -- are now actively courted.

"We have come a long way toward reconciliation," said one senior government official.

Hinton suggested that an elected government could adopt much more conservative policies than the present one, even to the extent of rolling back some of the U.S.-promoted economic reforms, such as nationalization of the banking system, without losing Washington's support.

Asked how far to the right the government would have to go before the United States would withdraw its backing, Hinton said any attempt to massacre the opposition on the scale of the 1932 suppression of a communist-led uprising by Gen. Maximiliano Hernandez Martinez, when 30,000 people were killed, would provoke a cutoff.

"They could go totally bananas and go back to the policies of general whatever-his-name-was who handled the 1932 situation," Hinton said. "It's utterly absurd that the United States would continue to support a government that adopted that kind of a policy to deal with the situation in El Salvador."

Even if conservative businessmen or their representatives are not actually brought into the present government, they will almost certainly be included, through new and old political parties, in the electoral commission and its decisions, according to current members of the government and the commission.

As preparations for the March elections continue, it becomes increasingly evident that all contending parties will be essentially conservative, running the gamut from the relatively centrist and reformist Christian Democrats now in the government to the right-wing National Conciliation Party, which dominated the country as the official military political front until the 1979 coup.

The socialist National Revolutionary Movement and communist National Democratic Union, both legally registered parties, are part of the guerrilla-allied Revolutionary Democratic Front. Now that the Front and the guerrillas themselves are officially recognized by Mexico and France as a "representative political force" that should be party to a negotiated settlement before elections, the chance of these leftists participating in March is even more remote than before.

Neither of these parties has ever demonstrated any large constituency of its own in the past, preferring instead to run in a coalition with the Christian Democrats in 1972 and 1977. But their participation would have provided some ideological balance to the contest.

The Socialists held some informal and inconclusive talks with members of the electoral commission early in the summer, according to commission member Ernesto Rodriguez Rivas. There was some speculation here that the Communists might form a new front party and participate just to keep their options open. But spokesmen for the Front flatly rejected involvement in the current process at a press conference in Mexico Friday after announcement of the Mexican-French declaration.

Although the Christian Democrats have the advantage of incumbency, and conservatives have accused them of trying to rig the elections, one party leader, San Salvador Mayor Adolfo Rey Prendes, estimated that the Christian Democrats will win at most 33 of the likely 54 seats in the constituent assembly and possibly as few as 25.

Christian Democratic leaders maintain that the very fact of a civilian government will introduce a "new generation of power" in El Salvador, since the Army previously controlled everything. The Christian Democrats, however, still do not expect to be able to control the Army, even if they win by a landslide.

Soon after the current government began to move toward elections last spring, military officers received a circular from right-wing activists warning that a Christian Democratic government endorsed at the polls would begin a series of war crimes trials against soldiers involved with death squad murders.

Most officers ignored the circular. There was no need for any of them, even those involved with the killings, to worry.

The Christian Democrats have learned through 20 months of coalition government with the military just how far they can take their influence over the Army.

"It is not possible to control the Army totally," one senior Christian Democratic official said privately last week.

Speaking of other Latin American countries as well as El Salvador, the official said many elected governments have "touched the privileges of the armed forces and have fallen for that. We couldn't push the armed forces too far because they have the arms, after all, and would react."

For the moment at least, the official said, the Army seems to have its hands full with the war and wants a civilian government, with many of the more liberal officers genuinely in favor of it.

"I think they will approve of a civilian government. And we the Christian Democrats are sufficiently intelligent to build for the future. We can look for mechanisms within the realm of the possible."