El Salvador's main left-wing guerrilla front announced today that it plans to merge its five separate forces into a single organization at some unspecified time in the future.

The top leaders of the Farabundo Marti National Liberation Front, known by its Spanish initials FMLN, issued a declaration that "we have achieved a level of unity in our political thinking so that substantial differences of a strategic character no longer exist." As a result, the statement said, it was agreed at a meeting last month "to advance to convert the FMLN into a single organization."

It was unclear how significant an eventual unification of the FMLN's forces would be. Salvadoran leftist civilian leader Guillermo Ungo, who is allied with the FMLN, said in a telephone interview that he doubted that such a merger would take place "in the short term."

A change in the FMLN's structure would not affect relations between it and the Democratic Revolutionary Front, headed by Ungo, which includes exiled civilian politicians. The FMLN and Ungo's group are formally allies but have disagreed over tactics.

U.S. officials predicted that a formal unification would not mask differences among the FMLN's member forces.

The announcement was issued in the name of the FMLN's general command, which comprises the top leaders of the FMLN's five guerrilla forces. It was made available in Mexico City by the Salvadoran left-wing news agency Salpress and was broadcast in El Salvador on the FMLN's clandestine Radio Venceremos.

A merger of the FMLN's forces could lessen differences between the two largest groups, the People's Revolutionary Army and the Popular Liberation Forces. The former is active mainly in the east and consistently has employed tougher tactics than the latter, which is based in the north-central sector.

The People's Revolutionary Army forcibly recruited hundreds of youths last year and kidnaped 17 mayors this year, tactics that have been avoided by the Popular Liberation Forces.

The agreement to move toward eventual unification was reached at a meeting of the FMLN's general command in July in Morazan province, according to the declaration. Northern Morazan is the site of the headquarters of the People's Revolutionary Army and of its leader, Joaquin Villalobos, who is considered to be "first among equals" in the FMLN's leadership.

But it was the Popular Forces' top commander, who goes by the pseudonym Leonel Gonzalez, who read the declaration on the radio. Some observers suggested that Gonzalez, whose real name is Salvador Sanchez, was selected to make the announcement as a sign that he was accepting the goal of unity.

The three smaller guerrilla forces in the FMLN are the Armed Forces of National Resistance, the Armed Liberation Forces and the Central American Revolutionary Workers' Party.