SAN SALVADOR, DEC. 14 -- A judge has ordered the release of two men jailed for the 1981 killing of two American land-reform advisers and the head of the program, ruling that their cases fall under a sweeping amnesty decreed as part of a regional peace plan.

Judge Rosa Maria Fortin said that if her ruling stands up on appeal, a pending case against a cashiered Army officer accused of ordering the deaths would be closed. She made her finding Friday, and it was made public today.

The decision was immediately appealed by the attorney general, with the support of the U.S. Embassy. Meanwhile, the two former National Guardsmen convicted in the case are to remain in jail. A ruling is expected in the new year, Fortin said.

The killings were one of El Salvador's most shocking and came as the government, supported by the United States, was implementing a sweeping land reform that stripped the landed rich of much of their economic base and infuriated the militant far right.

On Jan. 3, 1981, Americans Michael Hammer of Potomac, Md., and Mark Pearlman of Seattle, along with Jose Viera, in charge of the Institute of Agrarian Transformation, were gunned down by two men in the coffee shop of the Sheraton Hotel in the capital.

Hammer and Pearlman were advisers working with the AFL-CIO's American Institute for Free Labor Development.

In February 1986, Jose Dimas Valle Acevedo and Santiago Gomez Gonzalez, who confessed to being the triggermen in the case, were given the maximum sentence of 30 years in prison for aggravated homicide.

Both men said two proteges of rightist leader Roberto d'Aubuisson helped plan and ordered the killings. But under Salvadoran law, the testimony of a person implicated in a crime is not valid against another person involved in the same crime.

Both said former lieutenent Rodolfo Isidro Lopez Sibrian ordered them to carry out the killings and that cashiered captain Eduardo Avila was present and approved the action.

Avila was released in the case by the Supreme Court, where his uncle sits. While the case remained open, repeated efforts by the U.S. Embassy to move it forward have produced few results. If the present ruling stands, the case will be closed.

The case against Lopez Sibrian was closed, but he was arrested last year for participating in a right-wing kidnap-for-profit ring.

Fortin said in an interview, "It is my finding that this crime fits the legal definition of political crime and therefore falls under the amnesty enacted Nov. 5. If the purpose of the killings was to end the land reform, it was political, and if it was to kill a government official, it is also political."

A U.S. Embassy spokesman said, "We understand and respect the desire of the Salvadoran government to offer the most ample amnesty possible under the Guatemalan peace plan."

The plan, signed Aug. 7 by the five Central American presidents, included a call for a broad amnesty in countries with armed conflicts.

This is the second high-profile case involving American citizens to fall under the amnesty program. In November a military judge ruled that three men imprisoned for the 1985 killing of four U.S. Marines and two American technicians were covered by the amnesty.

The attorney general and the U.S. Embassy appealed the case, and it is now in the hands of a military appeals court.

Human rights groups harshly criticized El Salvador's amnesty law when it was passed because it would pardon those who participated in the tens of thousands of political murders carried out in the past eight years, usually by rightist death squads, as well as make it impossible to prosecute military officers for human rights abuses or the killing of civilians.

Under the amnesty, about 480 political prisoners, most suspected leftist rebels, were freed, angering the military and security forces.

Special correspondent Wilson Ring reported from Tegucigalpa:

An amnesty law that Honduras passed last month under the Central American peace process goes into effect Friday and is expected to result in the release of 28 peasants, most of them jailed for invading land in an effort to hasten application of a land-reform law.

In another development possibly affecting the regional peace plan, the Honduran Air Force is scheduled to take delivery Tuesday of the first two of 12 fighter planes purchased from the United States.

Both the amnesty and the expected delivery of one F5E fighter plus a trainer version follow an announcement by Sandinista Defense Minister Humberto Ortega over the weekend that Nicaragua plans to more than double its number of troops to 600,000.

Honduras and the United States say the F5s are needed to maintain Honduran air superiority that serves as a deterrent to the Sandinista military. The Honduran armed forces, including police, totals about 20,000 men.

Even though Nicaraguan President Daniel Ortega backed off Humberto Ortega's comments, saying the military buildup was not definite, the planes' arrival and the Sandinista announcement would appear to be blows to the peace process.

The F5s are to replace one-for-one an aging squadron of French-made Super-Mystere jets that were purchased by Honduras from Israel a decade ago.