Prince George's County's chief prosecutor, angered by the public release of a state police report that charged county officers with planning several convenience store holdups, two of which ended in fatalities, attempted to discredit the state probe yesterday, saying it was based on the word of "known thieves."

State's Attorney Arthur A. Marshall attacked the report, and Maryland Attorney General Stephen H. Sachs' decision to release it, only minutes before he was informed by state investigators that county police may have been involved in a cover-up during an internal county police probe of the incidents earlier this year.

Marshall said he has made no decision on whether to prosecute anyone in connection with the county probe. He said he advised the state investigator to give him a final report but not in writing "because I don't want to see it in the newspapers."

The prosecutor said he would be willing to present the case to a county grand jury -- an action he rejected some months ago as "inappropriate" -- or would invite Sachs to present the matter to a grand jury himself if the state official so desired.

"I think Sachs should put up or shut up," Marshall told reporters yesterday. "He should either charge where there are criminal offenses or he should apologize to the officers for releasing the report."

The internal police report on allegations concerning what was known as the "death squad" was ordered by County Executive Lawrence Hogan, who was responding to Washington Post inquiries. That report cleared the county police of any misconduct or wrongdoing.

The 40-page summary released a week ago by state police contained "major discrepancies" between their conclusions and the county's. There were also hints, which were carefully deleted before its release, of obstruction in the internal county probe.

The state report concluded that a small clique of officers had informants solicit persons to commit crimes, arrange details, then had the locations staked out. The state police said the officers who fired the fatal shots did not know how the crimes had come about.

Several informants interviewed by the state police passed lie detector tests, as did a former detective who provided additional details of events. The three "principal officers" involved, including the county's current acting police chief, refused to take such tests and were, "for the most part, unable to recall many of the details" of the cases, the state report said.

"I happen, as a matter of course, to believe police officers as opposed to criminals," Marshall said yesterday.

It was the informants, not the officers, he said, who "caused the death of some people, the injury of others, the arrest of others." However, survivors and others affected by the 1967 incidents are considering legal action against the police, they have said.

"If I were the informants," Marshall insisted yesterday, "I'd be concerned, because these are not the sweetest people in the world. There might be retaliation. I can see why these people are trying to blame someone else. If I were in their position, I'd want to blame someone else."

To get his points across publicly, Marshall released to reporters a packet of letters he wrote this week to Sachs, Gov. Harry R. Hughes, County Executive Hogan and Acting Police Chief Joseph D. Vasco, Jr.

Vasco, Retired Maj. Blair Montgomery and Capt. James Fitzpatrick, in charge of training county police, were cited by state police as the "three principal officers" involved in the incidents.

Marshall said there was no evidence to support criminal charges for the 1967 actions, although the same actions today "may be illegal."

"I for one," Sachs said, "thought there could be no criminal charges after 12 years, even if crimes were committed."

The decision to release the state report was made after consultation with Marshall, Sachs said.

"When local law enforcement is under acute public suspicion," Sachs said, "you can't invite in an outside agency of high credibility, read their report which has some extrememly critical things to say, announce to the public there's nothing wrong and expect that to be the end of the matter."