Recent Italian laws offering leniency to repentent terrorists who cooperate with police appear to have encouraged a top member of the notorious Red Brigades to confess, and brought about a major breakthrough against terrorism.

Information attributed to the confession of a 27-year-old suspected terrorist, Patricio Peci, has led to 45 recent arrests and to new charges against already jailed suspects. Peci is thought to have been a member of the Red Brigades' strategic command and a participant in the 1978 kidnaping of former prime minister Aldo Moro.

On the Italian police's most-wanted list for the last three years, he was the head of the Turin column of the Red Brigades until his arrest Feb. 19. Secret Service sources confirmed press reports here that Peci so far has supplied police with more than 60 page of names, places and dates.

Soon after his arrest, the sources said, Peci began providing tips that proved reliable, including information involving the location of arms used in various terrorist attacks. He is also thought to have provided information leading to a police attack March 28 on a Genoa hideout in which four alleged terrorists were killed and to the arrests the same day in Toulon, France of four other Italian terroists.

A police source described Peci's confessions as "a very severe below" to the Red Brigades organization. He suggested that a hiatus in terrorist activity in recent weeks may mean that the remaining members of the left-wing terrorist group are now on the run.

Most of the recent arrests took place in the Italian north -- particularly in Turin, nearby Biella and Genoa. Sources in Turin said the sweep may have destroyed the core of the Red Brigades operation in that area.

These sources said that confessions by Peci and other terrorists had supplied them with the names of the terrorists responsible for 27 major attacks in the area since 1976, including seven murders.

Speculation is now centered on why Peci confessed. Earlier press reports that he was convinced by his mother to do so have been denied by family members, who said Peci had had no contact with his family for two years.

Another theory is that Peci suffered a "crisis of confidence." But political sources with close government contacts say that Peci has been bargaining with authorities ever since his arrest, initially requesting both money and eventual release.

An Italian atiterrorism law passed in February promises repentant terrorists who cooperate with police that life sentences will be replaced by jail terms of from 12 to 25 years and other sentences will be reduced by a third to a half.

Press reports confirmed by other sources said Peci supplied details regarding the 1976 murders of Genoa District Attorney Francesco Coco and Turin Bar Association official Fulvio Croce, and the 1977 murder of a well-known Turin journalist, Carlo Casalegno, in which he himself participated.

Peci, now in a Pescara jail, allegedly has told authorities that the Red Bridgades strategic command included himself; two of the terrorists killed in the Genoa raid; Mario Moretti, nicknamed the Scarlet Pimpernel because of his ability to evade arrest, and Moretti's girlfriend Barbara Balzarani, also still at large.

A secret Services source said the Peci confession appeared to confirm the thesis that except for "operational contacts," there was no foreign involvement in Italian terrorism.

Reports regarding Peci's alleged role in the Moro kidnaping and murder are confused. Most papers here carried reports that Peci had admitted being part of command group that kidnaped Moro and killed his five bodyguards. There was also an unconfirmed report that Peci had revealed the location of the hideout -- reportedly a store in or near Rome -- where Moro was kept prisoner for 54 days before being murdered.

Although the new terrorism law is presumed to have facilitated Peci's confession, authorities have not revealed the details of any leniency agreement reached with Peci in exchange for his information.

An inside sources said recently that several other persons jailed for terrorist activities began turning state's evidence following passage of the new law.