For two years as the raging fires of revolution have spread through Nicaragua, El Salvador and Guatemala, fears have mounted that all of Central America would be engulfed. Until recently the fears were nothing more than that.

But there have been hints of trouble in Honduras and Costa Rica for several months and now a Honduran airliner has been hijacked to Nicaragua and at least 50 of its passengers, including several Americans, are being held hostage. In Costa Rica, a bomb has injured three U.S. Marines.

Use of terrorist tactics has erupted now in both countries, and although it is not on a scale even close to the warfare of El Salvador or Guatemala, it has shocked Honduras used to the most placid military dictatorship in the region and horrified Costa Ricans, who are tremendously proud of having the most stable democracy in Latin America.

The violence seems to be coming from groups with various ideologies. It springs partly from serious internal economic and political problems in each country, but it is also closely related to the atmosphere of fear that grips the entire region.

The immediate repercussions are felt more strongly in Honduras.

"What you're seeing is the emergence of a pattern," said one well-informed Western source. "The feeling now is that people are polarizing. The pot was already seething, now it is boiling."

There are numbers of violent factions on both left and right in Honduras and their exact strength is impossible to judge.

"The climate of violence has been growing," said liberal newspaper editor Manuel Gamero. "The problem of El Salvador is affecting us, and that is additon to our own problems of misery and poverty. Undoubtedly all this has caused the formation of radical groups. For some time we've noted the organization of anitcommunist bands threatening principally moderate groups."

A year ago political violence was virtually unheard of in Honduras. Under pressure from the Carter administration in Washington, the Hondurans elected a contituent assembly, and national elections are tentatively scheduled for November.

At the same time, however, the United States moved to beef up the Houndran military with $3.5 million in military assistance, at least 10 Bell Huey helicopters on a no-cost lease program, dozens of U.S. military trainers including counterinsurgency experts and more than $60 million in economic aid.

The official rationale for the program was to help the Hounduran military guard the country's borders and keep the Salvadoran conflict from spilling over. Opponents of the Salvadoran government have charged, however, that the United States intends to use Honduras as a surrogate military force for possible intervention in El Salvador and to cooperate with the Salvadoran military in border offensives against Salvadoran guerrillas.

Until the last six months, domestic terroist incidents in Honduras tended to be fairly insignificant and in some cases almost farcial. But the last six six months have been differnet. There have been several shooting and bombing attacks on various targets, mostly attributed to leftist opposition groups.

In mid-January a large arms cache destined for Salvadoran guerrillas was uncovered in the Honduran town of Comayagua, west of the capital, and several arrests were made.

Then on Friday a Honduran 737 jet bound for New Orleans was hijacked five minutes after leaving Tegucigalpa's Toncontin airport. The four hijackers are demanding the release of the prisoners taken after the Comayagua arms raid as well as Salvadoran leftist leader Facundo Guardado, whom the Honduran authorities deny is in their custody.

Costa Rica has maintained peace and democracy for more than 30 years, but there, too, extremism has begun to flourish amid serious political and economic crisis.

With its oil bill rising astronomically, the price of coffee down and the cost of its extensive social services growing burdensome, the government of President Rodrigo Carazo was already under severe political attack.

Much of the Costa Rican violence appears to come from the extreme right, which is led by a well-funded paramilitary group known as Movement for a Free Costa Rica. But there are leftist guns as well.

"Radio Noticias del Continente," a powerful left-wing shortwave radio station outside the capital of San Jose was attacked at least four times by rightist gunmen in the last years. On at least one occasion the occupants of the station returned the fire. The station was subsequently raided by the government and when automatic weapons were found inside it was shut down.

A courtesy visit by two U.S. Navy ships scheduled for earlier this month became a major political issue. The visit never took place, but in what U.S. officials say may be a related incident on Jan. 27 a van with three U.S. Marine embassy guards in it was hit by a homemade bomb in San Jose.

One U.S. analyst familiar with both Honduras and Costa Rica said he believed the timing of all these actions is largely coincidental. But, he added, "you can't discount either the possibility of Cuban connections or the romantic identification with revolution, the bandwagon effect." This is one bandwagon both Honduras and Costa Rica had hoped to avoid.