The trial is expected to begin this spring of two Salvadoran former National Guardsmen accused of killing two U.S. labor advisers in 1981, the chief prosecutor in the case and another Salvadoran court official said this week.

In addition, a government legal team is considering trying to reopen an inquiry into the role of Salvadorans who previously have been implicated as planners of the killings but recently were cleared, according to the prosecutor and another source familiar with the case.

Prosecutor Juan Castillo of the national attorney general's office said in an interview Wednesday that the panel was mulling whether to seek to transfer the investigation from civilian courts to military ones to accomplish this, but he said it was "only a possibility."

The planned trial and consideration of further inquiry are the two positive elements in the outlook for investigations of past cases of political violence in this country, according to Salvadoran and U.S. human rights activists and other observers. They cite these other developments in recent months:

*Judge Bernardo Rauda, who last year sentenced five other former National Guardsmen for killing three U.S. nuns and an American lay worker in December 1980 was transferred to a less desirable court last autumn.

Rauda said in an interview at his home that he suspected he was a victim of a vendetta by conservative court officials.

*Investigations appear stalled or have dragged on in several other prominent human rights cases, such as the gunning down of San Salvador Archbishop Oscar Arnulfo Romero in March 1980 and a well-documented case of the alleged armed forces killings of civilians two years ago in western El Salvador.

*Finally, Salvadoran disputes have blocked spending of $3 million of U.S. aid to assist El Salvador in reforming its judicial system.