Accused U.S. spy Michael Lance Walker had access to a so-called "burn bag" of secret documents on the nuclear aircraft carrier USS Nimitz, Navy sources disclosed yesterday as officials continued to investigate a case of espionage they said may have been more far more damaging to national security than originally suspected.

The most sensitive documents on a carrier generally are shredded, sources said, but other classified material is set aside to be burned. Documents in the burn bag could contain information on the movements of American and Soviet ships.

While Naval officials and intelligence analysts agree that the burn bag might have held sensitive information, they say that far more damaging material may have been provided to the Soviets by Michael's father, John Anthony Walker Jr.

The elder Walker, who was arrested Monday, had access to information about the movements of both U.S. and Soviet submarines and other ships as a radio officer on Polaris submarines and as a communications officer for the Naval Submarine Force, the Amphibious Force and the Naval Surface Force in Norfolk, beginning in the early 1960s. He had "top secret crypto" clearance before he retired.

Both father, 47, and son, 22, have been charged with espionage.

Navy sources said Barbara Joy Crowley Walker, John Walker's ex-wife and Michael Walker's mother, turned in her former husband, who had been working as a private detective in Norfolk since his retirement from the Navy in 1976. Barbara Walker, who is believed to be living on Cape Cod, could not be reached for comment.

John Walker was arrested in the Ramada Inn in Rockville after federal agents saw him dropping off a bag of documents in Poolesville in western Montgomery County. Michael Walker was arrested aboard the Nimitz on Wednesday, and he is scheduled to return to the United States today. Navy officials said Walker will be turned over to the FBI after he arrives at Andrews Air Force Base this afternoon.

Sources said yesterday that a Soviet national, spotted Sunday near the Poolesville site where agents recovered the classified documents, has left the United States.

The senior Walker, who is being held without bond in the Baltimore city jail, yesterday asked a federal judge to bar the FBI, Navy and other officials from revealing nonpublic information about the case.

But U.S. District Judge Norman P. Ramsey said he would impose the order only if U.S. Attorney J. Frederick Motz agreed. Such a limitation, Ramsey said, "has all the earmarks of a gag order."

John Walker's attorney, federal public defender Fred Warren Bennett, said after the hearing that he did not expect Motz to agree to the order, and that he would appeal the ruling to the 4th U.S. Circuit Court of Appeals, perhaps as early as Tuesday.

FBI officials said earlier this week that they believed that the motivation for the alleged espionage was financial gain.

Michael Walker had "secret" clearance aboard the Nimitz, where he held a clerical position in the ship's operations department. Walker's "secret" clearance was higher than "confidential" but lower than "top secret" clearance, officials said.

Michael Walker was assigned to destroy materials up to the level of "secret" in the "burn bag," Navy sources said.

Retired Adm. Eugene Carroll, deputy director of the Center for Defense Information, a Washington policy group, said that Walker's "burn bag" duty would permit him to see a much wider variety of material than a normal seaman.

Among the items found in a search of Walker's bunk area on the Nimitz was a box containing about 15 pounds of classified material, according to an FBI affidavit filed in federal court in Baltimore.

Carroll, whose organization is often critical of the military, said the most damaging information accessible to Walker would be intelligence about Soviet ship movements in the Mediterranean, particularly submarine locations.

It would be helpful, he said, for the Soviets to know how much the United States knows about the movement of Soviet submarines so they could develop tactics to elude detection.

The elder Walker knew even more. He could have passed on "spot information about where actual U.S. ships were deployed at any given moment," according to George A. Carver Jr., a former high-level official in the CIA and now a senior fellow at Georgetown University's Center for Strategic and International Studies. John Walker's alleged involvement was "potentially quite serious" for the United States, he said.

Carver said that information allegedly passed by Walker could have been used by the Soviets to make up their own fake communications.

Forgeries, he said, are "more plausibly done if you know . . . the salutation used and the way that the prose is used."

Information on submarines is considered "perhaps the most sensitive intelligence information that the United States has," said Capt. James T. Bush, a retired submarine commander who also works at the Center for Defense Information.

"The backbone of the deterrent philosophy is that the missile-firing submarines are invulnerable," Bush said.

"If that philosophy is changed, then we have to change a whole way of doing things."

According to Navy sources, attack submarines routinely lie in wait at ambush spots under the sea to pick up the trail of Soviet missile and attack submarines. The U.S. attack submarines are quieter than their Soviet counterparts, enabling them to tag after the Soviet boats at a distance without being heard.

In a war, the United States would try to sink Soviet submarines before they could go from port to the open ocean, Navy sources said. This tactic is part of the "barrier strategy" developed over the years to deal with the Soviet undersea threat. The secret papers could compromise some of the basic elements of this strategy, according to the sources, and prompt the Soviets to develop countermeasures.

"The elder Walker was the really grievous loss to our intelligence community, tragically so at the time," Carroll said.

Assuming that the information was sent promptly to the Soviets, he said, "it would have told them everything about our capabilities at the time."