A generation after a controversial trial in which three Greek Communists, were convicted or murdering CBS correspondent George Polk, two members of Parliament say that they have uncovered vital new evidence and plan to petition that the case be reopened.

The only material evidence the prosecution presented in the 1949 Salonika trial was an envelop in which Polk's prosecutors said that it had been addressed by the mother of one of the defendants, Gregorios Staktopoulos, then a part-time correspondent for Reuter news agency.

Staktopoulous was sentenced to life in prison, but his other was acquitted. Two other defendants, Vangelis Vasvanas and Adam Mouzenides, ranking members of the Greek Communist Party, were sentenced, in absentia, to death.

Today, at a press conference called by the two parliamentarians, both lawyears, they charged that American and British intelligence units participated in an elaborate coverup of the murder. Both services were heavily involved in trying to prevent a Communist takeover in Greece following World War II.

The lawyers dismissed Communist involvement in the murder, saying it clearly would not have benefited the Communists. Papathemelis said he suspects British Intelligence was responsible for Polk's death. The rationale? A Machiavellian plan to destabilize American-Soviet relations and to cause difficulty for the conservative government of Greece.

The attorneys presented two handwriting experts who said they were convinced that a Salonika grocer had addressed the envelope that had figured so importantly in the trial.

The lawyers said the grocer's widow, Mersina Karamichalis, 90, is prepared to testify that her husband addressed and mailed the envelope.

In addition to the envelope, the prosecution based its case against Staktopoulos, now in his 60s, on four rambling, often contradictory confessions he made. He now says the admissions were obtained after four months of torture and he has recanted them.

Staktopoulos' lawyers, Stelios Papathemelis and Gregory Papastergiou, say that much key evidence, including the envelope, is missing from the court files.

When Polk was killed, the nation was torn by a civil war between Communist and rightist forces. The commander of the Greek Communist army, ELAS, was Markos Vafiadis. Polk was on his way to interview Vafiadis when he was killed.

The two parliamentarians said reporters from the Salonika Daily Macedonia, where Staktopoulos also worked, are ready to testify that Staktopoulos was at the newspaper at the time he allegedly was leading Polk to Markos' mountain headquarters. The lawyers said none of the reporters was questioned during the police investigation of the murder.

Constantine Kallias, minister of justice from 1958 to 1961, reduced Statopoulos' sentence to 17 years and he was released in 1961.

"When I released Staktopoulos," Kallias says today, "many asked 'Don't you fear the American reaction?" I said I was sure the Americans have doubts about the guilt of Staktopoulos equal to my own."

Kallias became involved in the case after he discovered that for almost five years after he was convicted, Staktopoulos was not sent to jail. He stayed in isolation at the security headquarters of Salonika, under the supervision of security chief Major Nicholas Moushoundis, who also was the liaison with British Intelligence.

Moushoundis was Staktopoulos' main interrogator before the trial. Although he was kept in isolation, seeing no one but Moushoundis, the major occasionally took his prisoner to remote areas outside Salonika for meals and an occasional swim.

"It was most peculiar," said george drossos, a close friend of Polk. "The aim did not appear that Staktopoulos should suffer, but clearly that he must not speak."

If Stakopoulos is innocent, why was he picked as the scapegoat in such an eloborate coverup?

His lawyers pointed out that Staktopoulos was probably the only Greek journalist in Salonika who spoke English. Polk spoke no Greek and the presumption was, the lawyers said, that he would seek out an English-speaking professional colleague to be his guide and interpreter.

Staktopoulos also was a known leftist, although he had been taken off the Communist Party roster n 1946 for inactivity.

Papathemelis said. "Many other had been arrested and tortured before Staktopoulos. However, he broke under pressure and responded the best.

"The case has a bizarre history," the attorney concluded. "Considering the trumped-up accusations, Staktopoulos should have been sentenced to death. That he was not is in itself suspicious."

The lawyers said one of the other defendants in the case was killed during the civil war. The Greek government has refused permisson for him to return to Athens for a new trial.