Speaking for the rebels at Monday's meeting in La Palma will be top leaders of the Farabundo Marti National Liberation Front and its political arm, the Revolutionary Democratic Front. The coalition is often referred to by its Spanish abbreviation FMLN-FDR.

The FMLN is a coalition of five guerrilla groups formed in 1980. Washington estimates that it commands 9,000 to 12,000 fighters. It is believed to control between a quarter and a third of Salvadoran territory, but the area fluctuates as land changes hands between the government's forces and the guerrillas.

The two FMLN representatives at the meeting will be Joaquin Villalobos of the People's Revolutionary Army and National Resistance leader Ferman Cienfuegos.

The oldest member of the coalition is the Popular Liberation Front (FPL), founded in the early 1970s by a former baker and leader of El Salvador's underground Communist Party, Salvador Cayetano Carpio. The FPL established close links with activist priests and lay people espousing the Catholic Church's new liberation theology. Partly because of this connection, guerrilla influence and support spread rapidly throughout Chalatenango province, where La Palma is located.

The FPL is one of the two strongest guerrilla groups militarily, and its troops operate freely in Chalatenango and Cabanas provinces and many other areas of the country. In 1983 followers of Carpio knifed to death his former closest associate and FPL cofounder Melida Anaya Montes in Managua, the capital of Nicaragua. Shortly afterward, Carpio committed suicide. The new leadership remains shadowy, and the FPL's political influence within the guerrilla movement is said to have waned.

The FPL's rival for power within the coalition is the People's Revolutionary Army (ERP), also founded in the early 1970s as a small guerrilla group with a penchant for political kidnapings and other attention-getting military actions. By the late 1970s, however, it had gone through and rejected a Maoist phase and consolidated a dedicated peasant following in the northeastern province of Morazan, where liberation theology activists had also been active.

ERP founder and leader Joaquin Villalobos is generally acknowledged to be the FMLN's most daring and innovative military strategist. The ERP may have the largest army in the coalition. It is primarily active in Morazan, Usulutan and San Miguel provinces.

The National Resistance, broke away from the ERP in the mid-1970s, when Villalobos was accused of having ordered the assassination of Roque Dalton, a poet, historian and pro-Cuban Marxist member of the ERP who questioned Villalobos "militaristic" line. Dalton's fellow dissenters formed the National Resistance into a group with great influence in El Salvador's radical labor movement.

Through a series of spectacular kidnapings, the National Resistance soon became the wealthiest of the groups, enabling it to set up a well-equipped army. However, the National Resistance lags far behind the two larger groups in military power and influence.

The Central American Revolutionary Workers Party (PRTC) is the smallest and least known of the groups. It is an independent faction of a group originally founded with a vision of a united socialist Central America. When the FMLN's membership agreed to challenge the government on the battlefield in late 1980, the PRTC's role was largely confined to support activities. However, the group has grown and its leader, Roberto Roca, has consolidated his authority.

The Salvadoran Communist Party expelled its former secretary general, Carpio, in the late 1960s over the issue of guerrilla struggle, which the party opposed. In 1980, the party decided Carpio was right after all, and -- largely as a symbolic gesture -- set up its own armed group, the Armed Forces of Liberation (FAL), which joined the FMLN. The Communist Party's group is not known to have progressed in its military efforts, but the party is by far the oldest leftist organization in Central America, with a small but cohesive urban base. It was founded in the late 1920s by Farabundo Marti, who was executed on the eve of a failed mass uprising in 1932. The dictatorshp of Gen. Maximiliano Hernandez Martinez subsequently killed as many as 30,000 peasants accused of supporting the uprising. The FMLN takes its name from the founder of the Communist Party, while one right-wing death squad takes its name from the general.

The Democratic Revolutionary Front (FDR) is a coalition of several small parties and opposition groups, dissident labor unions and university associations. Both the Duarte and Reagan administrations have said it is a puppet organization, powerless and irrelevant compared with the guerrillas. But although it is true that the FDR's power base has dwindled during the leadership's prolonged exile and the long years of violence against its members in El Salvador, it is also generally thought that the influence of individual leaders within the FMLN-FDR has increased during the past four years of civil war.

Speaking for the civilian wing of the leftist coalition will be two former allies of Salvadoran President Jose Napoleon Duarte, Guillermo Ungo and Ruben Zamora.

Ungo, 53, is the head of the National Revolutionary Movement, a small party linked to the Socialist International. In 1972 he was Duarte's running mate in presidential elections as part of a broad coalition. The Duarte-Ungo ticket is widely acknowledged to have been cheated of victory by the military, which took over vote counting and proclaimed its candidate the winner.

Duarte went into exile and Ungo into relative obscurity, from which he emerged in 1980, when the original leaders of the FDR were kidnaped and assassinated by the Maximiliano Hernandez Martinez death squad. Ungo was designated to serve as the new FDR leader, and he has lived in exile since, pointing to the assassinations of the previous leaders as proof that it is not safe for him and his colleagues to live in El Salvador.

Ungo's association with Duarte goes further back than their 1972 campaign, however. His father was a cofounder of Duarte's Christian Democratic Party.

Zamora, 40, the other civilian to represent the left at the meeting, is a dissident Christian Democrat. He left the party in 1980, along with his position as minister of the presidency in the government formed after the Oct. 15, 1979, coup by officers who characterized themselves as reformist-minded. Less than four months after the coup, most members of that government had resigned, convinced that they were powerless to control the excesses of the armed forces, which had been firing on demonstrators and executing dissidents.

Zamora and several other young Christian Democrats resigned from their party in disagreement with Duarte's decision to make the Christian Democrats a key element in a second government. Shortly after Zamora's resignation, his brother, Mario, who was justice minister, was assassinated by paramilitary thugs in his own home.