Nicaragua's Sandinista government, faced with a mounting guerrilla challenge, has begun prosecuting ''counterrevolutionaries'' in a series of quickly assembled ''popular tribunals.''
The courts - whose findings are appealable but not to the Supreme Court, the one generally respected level of the judiciary - have become a new source of friction in United States-Nicaraguan relations.
The Sandinistas say that in the face of a US-sponsored ''invasion'' of their country, they need to take extraordinary measures to protect their national security. The tribunals are intended to help serve that purpose. But US critics contend that the courts mark a new stage in the Sandinistas' repression of domestic dissent.
The tribunals this week handed down their first verdict: a 16-year jail sentence to Freddy Bruno Herrera Perez, a truck driver charged with committing sabotage for the Nicaraguan Democratic Force. The FDN, which receives US aid, is fighting the Sandinistas on Nicaragua's northern border.
At the moment some 70 prisoners face tribunal proceedings that may result in sentences of three to 30 years. Their alleged crimes are said to run the gamut from taking up arms against the government to distributing counterrevolutionary literature to providing the rebels with a meeting place or food. The most celebrated case involves an alleged attempt to assassinate Interior Minister Tomas Borge Martinez. The attempt is said to have been directed by a man who once served as Borge's bodyguard.
Another group is accused of conspiring to establish an ''internal front'' to Eden Pastora Gomez's rebel group operating in the south of the country. According to an indictment, this band planned to set fire to a huge revolutionary mural in Managua's main plaza and to disrupt an anniversary celebration of Nicaragua's revolution by broadcasting one of Pastora's speeches.
Herrera Perez is one of a small number of suspects who are disillusioned revolutionaries; they fought on the side of the Sandinistas in the 1979 revolution, but came to believe the Sandinistas have deserted the goals of that revolt. Some others are former members of former dictator Anastasio Somoza Debayle's National Guard. A large number are residents of Nicaragua's Caribbean coast who did not fight on either side during the revolutionary struggle but have since become discontented with Sandinista rule.
About 10 percent are women, including a nurse accused of stealing medicine from a popular health clinic and giving it to the ''counterrevolutionaries,'' or contrasm as they are called here.
Sandinista officials said the need to respond to the activities of the counterrevolutonaries - some of whom had been in jail for as long as five months - was so urgent that they began the trials while workers were still plastering and painting the tribunals' new headquarters.
Both Western diplomats and Nicaraguan defense lawyers express qualms about the tribunals' ability to administer justice impartially, since two of the three members on each panel serve on Sandinista defense committees. ''Given the composition of the courts, I doubt you'll have any contras released for lack of evidence,'' a diplomat asserted.
The diplomats are concerned that although Nicaraguans tried by the new courts can appeal to a second panel, they no longer have access to the Supreme Court, perceived as the most independent and responsible of Nicaragua's judicial bodies.
Moreover, Nicaraguan defense attorneys claim that the definition of ''counterrevolutionary'' in the law is so broad that it could potentially be interpreted to include simple verbal criticism of the government.
For these reasons a high-level State Department official who recently visited Nicaragua informed Interior Minister Borge that the US considered the tribunals a potential threat to democracy. Borge responded that if the Reagan administration was not supporting an armed invasion of Nicaragua, the tribunals would be unnecessary.
Ligia Molina, president of the tribunals, says the Nicaraguan government is making every possible effort to give the defendants a fair trial, including provision for private attorneys free of charge.
With its potted plants and orange leather couches, the atmosphere in one of the tribunal offices - except for the presence of a couple of rifle-toting Sandinista soldiers - is reminiscent of any crowded waiting room. Relatives of the suspects chat quietly as they wait for hours to get a glimpse of the jailed loved one. Asked what the family member is accused of, they invariably respond ''cr'' - short for counterrevolutionary.
Most relatives openly proclaimed their family member's innocence, often citing as evidence a history of active revolutionary participation. One mother claimed her son, accused of participating in the plot to assassinate Borge, had just returned from a Sandinista-sponsored course in Bulgaria.
''In my house we're all with the revolution,'' she said.
Zoyla Zabar, whose nephew is charged with plotting to deface a revolutionary mural, said: ''My cousin just died in the mountains fighting for the Sandinistas. My son is in the Sandinista police. I don't know how they've confused us with the contras.''