Col. Adolfo Arnoldo Majano, widely regarded as the most liberal member of El Salvador's five-member junta, was forced out of the government today by a vote of the armed forces amid negotiations expected to restructure completely this embattled country's government.

Majano made it clear that he had not resigned voluntarily, and his political future was unclear.

Christian Democratic leader Napolean Duarte, another junta member, said today that he expects "many changes to take place" in the government in the coming week.

His party is negotiating with the military, and Duarte said that if "democratic interests" are not given complete control of the government and command of the military, the Christian Democrats will withdraw. The party holds two of the five junta positions and several Cabinet posts.

A special U.S. diplomatic mission arrived last night, led by Assistant Secretary of State for Inter-American Affairs William Bowdler and William Rogers, who held a similar post in the Ford administration. The team has been meeting all day with various factions of the Salvadoran government and military.

The mission was dispatched after the United States suspended more than $25 million in economic aid to El Salvador pending investigation of the brutal slayings last week of four American missionary women. Sources who have met with the diplomats say they clearly are interested in the entire chaotic political situation here, where the Carter administration has a major diplomatic stake.

Sources close to the U.S. mission said the Americans have taken a very hard line with the Salvadoran military, attempting to make clear under what conditions the United States would resume aid.

Despite recent Republican statements suggesting that there would be no major changes in policy toward El Salvador, the Americans appear to be encountering belief among the right wing here that when President-elect Ronald Reagan is sworn in, his administration is likely to support whoever is in power.

Washington has backed a reformist junta that took power 15 months ago and has sought to push the junta toward reconciling El Salvador's warring leftist and rightist factions. Recently, however, there has been a struggle for control within the ruling group, believed to have been encouraged by conservative politicians and business leaders.

Analysts believe the right has been encouraging the recent wave of political killings in hopes that they will lead to a right-wing coup. U.S. officials fear such a takeover could spark a wider confrontation in the region between the left and the right.

It is not clear, however, what the U.S. diplomats can do to avert what appears to be an evolving right-wing coup in El Salvador.

The ouster of Majano by a vote of the country's military commanders, who chose to have conservative Col. Jaime Abdul Gutierrez as their sole representative in the executive last night, is a clear first victory for the right.

Majano said this afternoon that he has not yet received official notification of the decision, but that he wanted it to be clear to the people of this increasingly polarized Central American country that he did not resign and will not resign.

Majano said the decision by the armed forces, "in these circumstances, leaves me free of commitments, and I can do what I choose."

There have been several reports that Majano has negotiated with leftists seeking to overthrow the government, but he declined to comment on his future plans.

Duarte left open the possibility that the Christian Democratic Party would withdraw from the government within a few days. He dismissed the ouster of Majano as being of little importance in the context of the current crisis.

"I think it is not important who is in or out. The most important thing is how can we solve the basis of our problems -- the violence," Duarte said. "Whoever has the capacity to do this should have the power to do it.

"If there is no solution," Duarte added, "we should leave the government. In order to control this county, [there must be] authority. That authority can come from the right or the left. We're proposing democratic authority."

[In another development, a Christian Democratic Party spokesman said the party has called for an exhaustive government investigation of the deaths of the four American women, Reuter reported.]

In an interview earlier today, Majano said the only way to reach a peaceful solution or at least a less bloody one to the political violence that has cost at least 9,000 lives here this year is to form a broad coalition government.

He welcomed, as have the Christian Democrats, the participation of outside governments as mediators in the current crisis. Both Majano and the Christian Democrats insist, however, that the final solution must come from internal forces and not be imposed by the United States or any other country.

Following a series of spectacular assassinations in which right-wing elements of the military allegedly were involved -- not only the murder of the missionaries, but of five internationally recognized leaders of the leftist opposition -- the chances for negotiation are steadily declining.

Majano told a reporter this morning that if negotiations do not bring results soon, then El Salvador's problems can be solved internally, "but it will mean putting on a helmet and fighting."