While the government here has given increasing indications of preparation for at least limited talks with its leftist opposition, that coalition of guerrilla and political forces has been struggling to present itself as a unified bargaining unit.

Although the official U.S. and Salvadoran government position remains that the only subject open for discussion is that of the left's participation in upcoming elections, the guerrillas have proposed a flexible agenda, with democratic elections only one of the goals.

Beneath the ongoing and still indirect dispute over what the talks might cover is the contention of the two governments that the guerrilla coalition is too divided to make talks worthwhile, with too many radical Marxist components, directed by Moscow, that cannot be trusted.

The extent to which the guerrillas have overcome their divisions ultimately may decide the outcome of any negotiations. The development of the Salvadoran left during the past 15 years, from its diverse roots in the Communist Party, the social and Christian democratic intelligentsia and one side of the Catholic Church, is a story of deep and sometimes murderous ideological schisms.

After forming a nominally united front in 1980, the five guerrilla factions until recently waged a war designed by a committee, carried out by separate forces under different commands and dependent for coordination on a consensus that often did not exist. Today, the guerrillas say they are together not only in their negotiating stance, but on the battlefield as never before. "In practice," said one senior figure in the rebel movement here, "in the mountains, there already is a unified command."

Away from the widening fire zones, ideological differences among the groups still appear passionate and potentially deadly. Only two months ago, one leader in the largest rebel faction murdered another and a third, the group's founder, reportedly committed suicide. But the guerrillas insist that was the end of a serious division, not the beginning.

Despite the microscope of international scrutiny under which the rebels have operated over the past two years of the intensified war, their differences and similarities are little understood outside their own secretive ranks.

Robert S. Leiken, a senior associate at the Carnegie Endowment for International Peace in Washington who has done extensive research on the Salvadoran left, recently pointed out, for instance, that a major argument used by Washington and the Salvadoran government in opposing talks with the rebels is that "the Marxists have the guns" and are assumed to be Soviet pawns. Yet the groups that have the most fighters among the rebels are those with a history of opposition to the Soviets and suspicion of the Cubans.

That most of the rebel movement's leaders consider themselves Marxists has been, in fact, a source of friction rather than unity. There is a religious intensity to their debates about whose line is more correct. Tracing details of the complex schisms and affinities is like studying schematic diagrams through a kaleidoscope.

When Salvador Cayetano Carpio founded the first of El Salvador's rebel groups on April 1, 1970, he was 50 years old. His background was proletarian. Having run away from a Catholic seminary at 12, he had been a laborer, a baker and a union organizer. He joined the Communist Party in the late 1940s and rose to be its secretary general.

Cayetano Carpio has said the revolution in Cuba and then the war in Vietnam convinced him that the only way to bring about a real revolution here was by force of arms. When the party, then dominated by the Soviet line favoring detente, refused to go along, he broke away. As "Marcial," he began building his Popular Liberation Forces (FPL in Spanish acronym) with other dissident communists, members of the persecuted labor movement and increasingly radicalized "base communities" of Catholics who had adopted the "theology of liberation."

Cayetano Carpio styled himself as the Ho Chi Minh of Central America, and he and his organization developed messianic attitudes, an intense if not fanatical dogmatism based on his reading of Vietnam's experience. "You have an idea what a communist formed in the time of Stalin is? That was Marcial," said a member of the guerrilla movement.

But while the FPL was being pulled together in the working-class neighborhoods of San Salvador and among groups of landless peasants, another group of revolutionary leaders was taking shape at the National University among the sons and daughters of the small middle class.

Student organizations of Christian Democrats and social democrats as well as young Communists were flourishing in the late 1960s. There were liberal nationalists, Maoists, Trotskyists, disciples of Ernesto (Che) Guevara and Fidel Castro.

In 1970, a loose collection of revolutionary students and some disillusioned Christian Democrats known as "The Group" carried out the first of what would be a long series of kidnapings during the next decade. From "The Group," according to leftists who knew its members personally, came the nucleus of the People's Revolutionary Army, the ERP.

After fraud by the military in the 1972 presidential elections led to widespread frustration with conventional politics, the ranks of guerrilla sympathizers swelled. Divisions also developed quickly.

Joaquin Villalobos, who exiled Christian Democrats now say had been a member of Catholic Action and their student organization, was a leader of the "militarist" faction. It contended that insurrection could be sparked by dramatic armed attacks on the existing power structure. Influences ranged from West Germany's Baader-Meinhof group to the Maoist Gang of Four in China. In 1975, according to Leiken, the People's Revolutionary Army briefly established official relations with the Chinese Communist Party.

Poet Roque Dalton, 39, a relative newcomer to the guerrilla ranks after years of living in Cuba and traveling in the Soviet Bloc, became the head of the "political" faction in the People's Revolutionary Army that emphasized the preparation of "the masses" before beginning major armed actions and the development of broad coalitions with other groups.

The "militarists" reportedly passed death sentences on the "politicals" and on May 10, 1975, Dalton was killed, accused not only of working for the CIA but also of working for the Cubans. His followers formed the Armed Forces of National Resistance (FARN).

A third split in the ranks of the erstwhile student leaders was led by Francisco Jovel, known as Roberto Roca. While living in Costa Rica, he took up the stance that there could be no successful revolution in Central America if it did not involve the entire region.

Jovel created a group known as the Central American Revolutionary Workers' Party (PRTC), intended to promote this cause in all five countries. But the success of Nicaragua's insurrection seriously undercut his organization's reason for being and, according to senior members of the rebel movement, the PRTC had to abandon its overt regional affiliations before it was allowed to join the overall guerrilla front in 1980.

By then, even the Communist Party under Shafik Handal had abandoned its opposition to armed struggle and joined forces with its former dissidents. The Sandinista victory in Nicaragua a few months before was an inspiration. Insurrection appeared imminent, and unity seemed to be the key.

The guerrillas formed the fledgling Farabundo Marti National Liberation Front (FMLN), joining their armed units in a loose coalition presided over by all five commanders.

But their real strength in 1980 lay in their "mass organizations," unarmed political fronts made up of students, workers and peasants.

The Revolutionary Coordinator of the Masses was created to bring together these groups. This in turn allied itself with the Democratic Front--Christian Democrats who had resigned from their party rather than serve in the government formed in January 1980, social democrats led by Guillermo Ungo and a small association of professionals. The marriage of these two umbrella organizations created the Revolutionary Democratic Front (FDR).

By the spring of 1980 the FDR-FMLN, through the mass organizations, was able to put tens of thousands, even hundreds of thousands of people into the streets. Their labor unions could paralyze the country. Victory seemed near.

But it did not happen. There were not enough arms and there was not enough coordination. Jealousies and enmities remained strong. Cayetano Carpio found himself seated beside the Communist Party officials against whom he had rebelled a decade before.

Meanwhile, the new U.S.-backed government promised reforms almost as sweeping as anything the guerrillas had offered, while its security forces and death squads set about systematically eliminating suspected rebel sympathizers.

The rebels now concede that by the time they had the guns and overall organization to launch an insurrection in January 1981 they no longer had the active popular support they needed. "What happened was that we lost the propitious moment," said Villalobos in an interview with leftist Chilean journalist Marta Harnecker late last year.

In a booklet called "Our Struggle for Peace," written in large part by Villalobos and exiled Christian Democrat Ruben Zamora of the FDR, the rebels talk about "the ebbing of the masses" after May 1980 as agitation and organizing fell off.

The popular organizations were crushed, and the rebels were not able to protect them. For all the talk of armed struggle in the previous decade, not one of the groups had put together an effective armed force.

They retreated to the mountains--the FPL to its traditional strongholds in Chalatenango, the ERP to Morazan and the National Resistance to Guazapa Volcano--and began to build serious fighting forces. But despite attempts to reach agreement on strategy, the rift widened between the two biggest factions, those of Cayetano Carpio and Villalobos.

But 1 1/2 years after the failed "final offensive" there were crippling disagreements over how to confront the elections of March 28, 1982. Villalobos planned a major offensive, perhaps one that could spark an insurrection. The FPL did virtually nothing to help.

Villalobos complained to Harnecker that March 28 might have been "the beginning of a debacle" for the government if the rebels had made "an audacious commitment of its force, not a commitment of 10 percent or 15 percent . . . ."

The military and propaganda defeat suffered by the guerrillas after the election forced changes. Villalobos said that with the elections over, the need to subordinate military actions to political ends had passed. "Our fundamental problem then became: How do you to break the Army militarily?"

The forces of the five factions began to work with increasing coordination, picking up momentum with a series of offensives that began last October. The joint military push was timed to coincide with a concrete offer to negotiate that the government, predictably, rejected.

By then, major changes were going on inside the FPL, according to senior members of the guerrilla movement. Cayetano Carpio continued to advocate his rigid approach to the war, but he was increasingly overruled by his field commanders and his second in command, Melida Anaya Montes, who leaned to the coordinated military strategy and tactics that Villalobos had advocated. At a January meeting of the FPL's Central Command, Cayetano's line was voted down, according to sources on the left.

Three months later, Anaya Montes was murdered in Managua, Nicaragua, allegedly by another FPL leader often described as "like a son" to Cayetano Carpio. The old founder of the FPL is said, then, to have committed suicide. Guerrilla spokesmen in exile and FPL fighters in the field insist that little changed as a result. The commitment to coordination already had been made and the vast majority of FPL commanders, they say, had supported it.

Washington and the government here have long hoped to split the moderates within the FDR away from the FMLN, but Leiken suggests that because of "interpenetration" recently "the whole idea of drawing distinctions between the democratic and violent elements in the Salvadoran left is becoming . . . irrelevant."