The government of El Salvador, seeking along with the Reagan administration to deflect calls in the U.S. Congress for a political solution to the Salvadoran civil war, is considering a speedup of its democratic elections to demonstrate a willingness for reconciliation with leftist rebels.

Reagan administration officials have been negotiating secretly with the government of President Alvaro Magana about announcing arrangements as soon as possible for new presidential and legislative elections in El Salvador that otherwise would not be held until next March.

U.S. government sources said last night that it is "a possibility" that Magana could make such an announcement Sunday, during the visit to El Salvador of Pope John Paul II.

The sources sought to portray any move Magana decides to make as "a Salvadoran initiative." But they also confirmed a Florida television report last night that former Florida senator Richard Stone, who has joined the Reagan administration as a high-level adviser on Latin American and Caribbean affairs, has been negotiating about this with political leaders in El Salvador.

They also confirmed that the Reagan administration was ready to welcome an announcement by Magana as a demonstration of the willingness of the government of El Salvador to offer the rebels an opportunity to stop fighting and seek a share of power through the democratic process.

While refusing to comment directly, one senior U.S. official said last night this "sounds very consistent" with the administration's position that all efforts should be made to "open the Salvadoran political process to all comers willing to play by democratic rules" but to oppose any negotiations enabling the guerrillas to attain power as a result of their military activities.

Elections were held last March in El Salvador, with substantial U.S. encouragement and assistance, to achieve much the same goal. But the guerrillas refused to participate, maintaining that elections held under the auspices of the rightist regime would not be fair or safe.

The large turnout for those elections nevertheless impressed the U.S. Congress and gave the Reagan administration more time to continue trying to help the Salvadoran army keep the rebels at bay while shaping a viable democratic government.

But the situation in El Salvador has since deteriorated because of political rivalries within a rightist-dominated transitional government, which is a coalition in name only, and a string of guerrilla military gains.

The assessment by the U.S. Embassy in San Salvador has been that a restructuring of the government and military is increasingly urgent to avoid a total collapse. This coincided with increasing congressional criticism here of the Reagan administration's policy in El Salvador.

Continuing a vigorous administration effort this week to persuade Congress to approve a $60 million increase in U.S. military aid to El Salvador this year, Thomas O. Enders, assistant secretary of state for inter-American affairs, said earlier yesterday that the alternatives were "anarchy" and dangerous rebel gains.

Enders also confirmed that the administration plans to increase the number of U.S. military advisers in El Salvador from the 37 or so there now to about 55. But he said there are no plans to go beyond that "self-imposed, informal ceiling" and there is no change in the policy of restricting the advisers to noncombat roles.

Enders said that, while "the fighting would go on for a long time," failure to provide more U.S. military aid this year would allow the guerrillas to start holding small towns against the government and no longer merely to overrun them temporarily.

Testifying before the House hemispheric affairs subcommittee, Enders used rhetoric reminiscent of the Vietnam-era "domino theory" to assert that "major national interests of the United States are at stake." He warned that if El Salvador's government is "knocked off," Cuban-backed communist subversion would surge north and south through the hemisphere.

"No government in the Central American isthmus will be safe," he said. "Nicaragua's Cuban- and Soviet-supported 'revolution without frontiers' would spread. It would head south across Costa Rica, which has no army, toward the Panama Canal. It would head north, putting enormous pressure on Honduras and reviving the guerrilla war in Guatemala and moving toward the Mexican border. So the struggle would go on, but on battlefields where the stakes would be much higher."

Explaining Reagan's decision to reassess the role of the advisers in a larger review of Central America policy, Enders said, "We are going to make an attempt to use that self-imposed ceiling more effectively. We certainly are heading in that direction."

But, he stressed, "We are going to use this ceiling first before we reassess the situation and see if more are needed later. In any case, there will be no change in their role."

Enders repeatedly insisted that failure to obtain the requested amounts would have "a very demoralizing effect" on the Salvadoran military's ability to combat the rebels. "There is never a good time for friends whose freedom is under attack to run out of ammunition," he said. "But this is assuredly the worst time.

"If there is no more military assistance this year, we would see anarchy in El Salvador, and no program, amnesty for the guerrillas or otherwise, would work . . . . I do not think we would see an immediate guerrilla victory, because the people would go on fighting, but there would be anarchy."

The administration's negotiations with El Salvador were first reported last night by correspondent Mark Feldstein of WTSP-TV of Tampa, who overheard Stone and two National Security Council aides discussing them on a flight from San Salvador to Miami. Feldstein said they were working on a statement to be issued in response to an announcement by Magana.

Feldstein said Stone told him the negotiations had reached "a very advanced stage," but later tried to talk Feldstein out of reporting the story on the grounds that it could jeopardize any administration agreement with the government of El Salvador. Stone could not be reached for comment last night.