El Salvador's guerrillas are threatening to take their war into neighboring Honduras to counter what they charge are increasing cross-border actions by Honduran troops working in coordination with the Salvadoran Army against rebel-held strongholds along the frontier.

In an interview here, Eduardo Solorzano, a member of the guerrilla front's 15-person "unified" military directorate, also said that crippling internal frictions among the five rebel factions have been patched up for the moment. The resulting unity, he said, has allowed them to defeat the government forces in a number of recent actions and to mount the coordinated guerrilla military actions now taking place across El Salvador.

Solorzano, who is the number two commander of the National Resistance faction, was joined in the interview by two other senior members of the same group, Jose Rodriguez Ruiz and Misael Gallardo. They said they were speaking in the name of the entire guerrilla front.

The guerrilla spokesmen said their goal is to keep up a high level of fighting and economic sabotage within El Salvador until "something gives" to break a current military stalemate and the U.S.-backed government is forced to negotiate. A key to this process, they said, is the role of the U.S. Congress and a possible cutoff of U.S. aid--now frozen pending Reagan administration certification that the Salvadoran government is promoting reforms and stemming human-rights abuses.

"Without the Congress there are no negotiations," said Rodriguez Ruiz. "We're fighting a very important battle among the American people."

The possibility of the war spreading throughout Central America has been a concern, a threat and a propaganda tool repeatedly employed by the area's revolutionaries.

The issue has garnered particular attention as the United States has accused Cuba and the Soviet Union of conspiring to subvert the region. Washington has increased military aid to Honduras from $3.6 million in 1980 to $10.7 million this year, with $15 million earmarked for 1983. U.S. advisers visit frequently, with as many as 90 being there at a time.

Solorzano and other guerrilla commanders now say as many as 2,000 Honduran troops have moved into El Salvador, beyond the so-called "pockets" of territory claimed by both countries since a brief 1969 war between the two. He termed the action "so arrogant and overbearing" that it accelerates the spread of the war and "obliges" the guerrillas "to act militarily in Honduran territory."

Honduran Army spokesmen said earlier this week that they have increased their military presence near the border, but they insisted that they have not gone and will not go into Salvadoran territory, nor become directly involved in El Salvador's civil war.

One senior Western observer reached by telephone in Honduras noted, however, that the pine forests along the border are so rugged that it is often difficult to determine whether a crossing has been made. Little independent information emerges, and according to officials from international agencies concerned with the frontier, the Honduran military now has declared the sparsely populated mountains a "restricted military zone."

Solorzano said the guerrillas previously were able to avoid direct clashes with the Hondurans, but recently there have been some small confrontations and an undetermined number of casualties.

Despite the rebels' failures to carry out threats in the past--notably their failed "final offensive" in January 1981 and their vow to stop the March 28 elections--they already are believed to have caused trouble in hitherto peaceful Honduras.

Government officials there and in El Salvador have long maintained that armed Salvadoran insurgents regularly use Honduran territory as a refuge, and that Honduran territory is a major route for guerrilla arms shipments.

Solorzano's "warning," moreover, comes after repeated assertions by Honduran officials that the Salvadoran guerrillas support and direct newly surfaced revolutionary groups allegedly responsible for three major kidnapings and two hijackings in Honduras since late 1980.

Ruiz denied direct ties to the Honduran revolutionaries. "Our own forces can operate in Honduras," he said. But he added, "Obviously, all the revolutionary organizations in Central America have solidarity, one with the other."

The guerrillas, who repeatedly have sought international recognition both by direct appeals and by offers to talk with established regimes, said they would be willing to negotiate with the Honduran government to end the problem.

After the massive turnout in El Salvador's March 28 elections handed the rebels a serious propaganda defeat, and once again showed them incapable of shutting the country down, the guerrilla leadership fell back into a long-established pattern of bickering and backbiting, according to various leftist sources.

"We are not going to deny that there have been some differences," Ruiz said in the interview. Asked if the differences kept the guerrillas from mounting any new coordinated action between March and May, Solorzano said, "That is true."

Some moderate leftist allies of the guerrillas say that a key dispute has been over the question of alignment with the Soviet Union--with the National Resistance, Peoples' Revolutionary Army and the Central American Workers' Party opposed to strong links with Moscow and the Popular Liberation Front and Communist Party favoring such ties.

Another difference lies in tactics. Solorzano's group favors extensive political and organizational work with civilians while other factions are more inclined toward strictly military operations.

Solorzano described as very effective the current military strategy of hitting the Army in different places in rapid succession, while at the same time destroying the economic infrastructure of the country. But he and the other spokesmen said its intent is to bring about negotiations, not the destruction of the Salvadoran Army.

Showing a new-found confidence after the recent string of operations, especially the 26-day fight for northern Morazan province in which heavy casualties were inflicted on the government, the guerrillas offered studied criticism of U.S.-trained battalions.

They suggested that the Ramon Belloso Battalion trained at Ft. Bragg, N.C., suffered from the fact that most of its troops were of middle-class urban origins and receive a higher salary on a longer contract than other soldiers. U.S. officials have portrayed these factors as virtues. The guerrillas say they result in troops who fight like mercenaries rather than committed soldiers.

For their tactics to be successful, said Ruiz, the Salvadoran Army would have to initiate massive bombing, deploy quickly in terrain that they knew well--unlike the troops in Morazan operating in territory they had never seen--and they would require more popular support than they appear to enjoy.