An informant for the secret police of ousted dictator Anastasio Somoza was the first to receive sentencing among an estimated 7,500 political prisoners awaiting trial by the new government here.

Neither the defendant nor his attorney was present last weekend when a three-member special tribunal sentenced Emilio Paez Bone to 30 years, the maximum penalty under law.

The sentence was read before a handful of reporters and a camera crew from the government network in a small, sparsely furnished room in one of the two suburban houses, confiscated from officers in Somoza's National Guard, where nine special courts hold their sessions.

Earlier, Paez Bone had presented oral testimony, as have all of the more than 60 prisoners who have appeared before the tribunals since they began hearing cases last month. The United States and others are carefully watching the trials as a means of judging the guerrilla government.

Last weekend's sentencing was typical of the informal way the trials are conducted. While they are closed to the public, anyone with a press card can stroll into a courtroom at any time to listen to testimony and talk to the prisoners.

Most of the court proceedings are written rather than verbal, and the press has free access to all documents. Defense lawyers and prosecutors answer questions freely, and only the court's deliberations when deciding the verdict are held behind closed doors.

The thick stack of documents in the Paez Bone case included affidavits from character witnesses, his oral testimony and documents from the files of the Office of National Security, Somoza's secret police.

The files, which apparently carried the most weight with the tribunal, show that Paez Bone had been an imformer for the secret police since 1959. Several documents from the Somoza government describe how he seduced a secretary who had ties to the Sandinista guerrillas and reported to the police the names of people she said were involved in the fight to overthrow Somoza. One of the secret police reports described Paez as dangerous and "of low moral character."

Although no concrete evidence was presented that any of the people he had informed about were killed. Paez Bone was convicted of mass murder, criminal association and instigation of crimes.

"Many people just disappeared and were never heard from again," tribunal member Jenny Gallo de Vigil, a lawyer, said. "We cannot get concrete proof of most of the deaths. The Office of National Security was organized to commit crimes."

Very few Nicaraguans have expressed sympathy for the thousands of prisoners, most of them members of the hated National Guard, who were jailed after the Sandinistas defeated Somoza's army last July. Reports of atrocities by the Guard, and especially the secret police, are generally believed even by people who do not support the new government.

The testimony of the prisoners, the majority of whom have denied all charges against them, is reported in great detail, but in a very skeptical tone, by the local media.

"The parade of 'little angels' continues," said one headline in the independent newspaper La Prensa. In news stories, the prisoners generally are called "henchmen" or "criminals."

Interior Minister Thomas Borge, who was jailed and tortured by the Somoza government for his Sandinista activity, told reporters that he talked to some of the "criminals" until 4 a.m. one night last week.

"I showed them the scars that were visible from my torture, and asked if they did not remember seeing me naked and bleeding," he said. "They have very bad memories."

Feeling against the former guardsmen is so strong that the trials are closed to the public because, as one court official said, "We don't want groups from the slums coming in here demanding the prisoners' heads." The slums of Managua were the site of heavy fighting and were bombed by National Guard aircraft just before Somoza fell.

So far, few prisoners have been released. Special prosecutor Nora Astorga said she has freed 53 for lack of evidence. The Interior Ministry has freed about 100 more, according to press reports.

Mario Mejia, coordinator of the trials, said Astorga has "bombarded" the tribunals with 20 new cases this month in an effort to relieve the bottleneck of prisoners. Mejia said he has asked the ruling junta to name six more three-member tribunals.

La Prensa reported that the Inter-American Human Rights Commission and Amnesty International have been invited to send observers to the trials and are expected to do so in the near future.