In a story spiced with foreign intrigue unpursued clues, MORE magazine has charged that the Greek and American governments and a distinguished group of journalists worked together 29 years ago to conceal the truth about the murder of CBS radio newsman George Polk.

A story in MORE's May issue, released yesterday, suggests that Polk, who was shot in Salonika in 1948 while covering the Greek civil war, may have been killed by rightist pro-government forces rather than by the Communist rebels who were convicted of the murder.

Yiannis Roubatis and Elias Vlanton, the Washington-based free-lancers who wrote the story, draw the conclusion from an intriguing collection of evidence that includes a telltale lobster shell, a disappearing British agent, and a "whistling bullet" that couldn't have whistled.

The story says the American State Department pressed for prosecution of the Communists, despite meager evidence against them, to shore up public support in the United States for then-President Truman.

Truman backed the right-wing Greek regime in its fight against the Communist insurrection that swept the Greek peninsula after World War II.

Polk was 34 in the spring of 1948 when he went to Salonika to look for the hideout of Markos Vafiades, the leader of the Communist guerrillas.

According to the Greek government's explanation of the murder, Polk fell in with Gregory Staktopoulos, a Salonika newspaperman who had connections with the Communists. Staktopoulos agreed to lead Polk to Markos' headquarters.

The government version says Polk was bound and blindfolded and placed in a rowboat in the dark of night for the trip to see Markos. But Polk never arrived. Greek prosecutors said Communists shot him in the boat and threw his body into Salonika Bay, where it was found a week later.

On the basis of that scenario - some of it drawn from confessions by Staktopoulos - Staktopoulos and two Communist leaders were convicted of Polk's murder in a Greek court in 1949.

The State Department accepted that verdict and pronounced the case closed.

So did a special committee established by a group of journalists, including Walter Lippmann, James Reston, and executives of The Washington Post and the Star, to investigate Polk's murder.

The MORE article says Lippmann, who chaired the committee, ignored contradictory evidence to produce a report on the case that "endorses the 'solution' . . . put forward by the Greek prosecutors."

The article in MORE says the prosecutors' solution is full of holes.

It bases that conclusion largely on recent interviews with James Kellis, a former Air Force officer who was sent to Salonika bythe journalists' committee in 1948 to investigate the murder.

Kellis told the MORE authors that he was suspicious of the evidence against the Communists accused of the crime. But when Kellis pressed his own view, that rightist elements had murdered Polk, the State Department directed the Air Force to bring him back to Washington, the article says.

Kellis had been pursuing the tracks of Randall Coate, a British information officer in Salonika. The MORE story says Coate left Salonike, never to return, within days of Polk's murder.

In Coate's quickly vacated house, the story says, police found a lobster shell. Polk had eaten lobster an hour before his death, an autopsy showed.

The story says Constantine Hadjiargyris, a Greek reporter who knew Polk, wrote a book on the murder in 1975 that also pointed to Coate as the culprit.

The MORE story also points out apparent contradictions in the confession made by Staktopoulos, the Salonika newsman.

Among othre things, Staktopoulos told the court he heard the "the whistle of a bullet" when Polk was shot. But the autopsy showed Polk was shot by a gun held tightly against his skull. the story says.

Staktopoulos, claiming he had been tortoured, recanted his confession in 1956 and has been demanding a new trial ever since.

MORE contacted some of the journalists who served on the Lippmann committee.

Columnist Marquis Childs said he was convinced in 1948 the Staktopoulos trial was a "cover-up" and he is happy to see the facts come out.

Reston, of the New York Times, said, "I don't really remeber if I was a member of the committee, but I'm told I was . . . Anything that indicates that governments have been fiddling with the truth ought to be exposed."