A congressional conference committee considering the Defense Department authorization bill is expected to approve measures permitting the execution of spies under military law and giving the Pentagon broad powers to use lie detector tests, according to key committee members and sources familiar with their deliberations.

Congressional sources said the conferees had tentatively agreed to adopt a House provision permitting the execution of military personnel convicted of espionage during peacetime. The Senate bill did not contain a similar provision.

Under current military law, the maximum punishment for espionage during peacetime is 10 years. Military law provides for a mandatory death penalty for spying during wartime, but the constitutionality of that provision is in question.

The sources said a panel of the full conference committee had voted to recommend continuation next year of a year-old pilot program permitting the Pentagon to conduct 3,500 "counterintelligence" polygraph tests on employes cleared to see the most sensitive category of classified information.

The panel also recommended that, beginning in fiscal year 1987, the Pentagon be permitted to subject to lie detector tests any of the more than 4 million military and civilian employes cleared to see classified information. Those seeking security clearances could also be required to take polygraph tests.

Congressional action on the death penalty and lie detector measures followed the arrests of retired Navy communications specialist John Anthony Walker Jr. and three other Navy men on charges of spying for the Soviet Union.

The full conference committee, scheduled to conclude its work this week, is expected to accept the panel recommendations. The full House and Senate would then have to act on the final version of the fiscal 1986 authorization bill.

The House last month passed a sweeping amendment, proposed by Rep. C. W. Bill Young (R-Fla.), permitting the broad polygraph program to begin immediately. The compromise endorsed by the panel essentially would adopt the amendment but delay its implementation for a year, and remove a provision requiring polygraphs before issuance of new clearances for employes to see the most sensitive information.

Pentagon officials had expressed concern about that the mandatory polygraph program would not give them adequate flexibility to determine where to use their limited number of polygraph examiners.

"We would like to have authority to use it in our program in the way we see fit," L. Britt Snider, the Defense Department's director of counterintelligence and security policy, said in a recent interview.

As of last month, the Pentagon had conducted only about 300 of the 3,500 "counterintelligence" polygraphs authorized by Congress, Snider said. He said officials were hoping to have conducted about 600 of the tests by September.

There are 152 polygraph examiners working for the Pentagon, which wants to train another 40 to concentrate on conducting polygraphs for security clearances, Snider said. "We are just going to have such a small capability for some time to come," he said.

On the issue of the death penalty, congressional sources said the conferees were still debating a provision in the Senate bill that requires a sentence of either life in prison or death for those convicted in civilian courts of spying for the Soviet Union or one of its allies.

Proposals to reinstate the death penalty for espionage in civilian courts have stalled in the House Judiciary Committee in recent years. Passing the provision as part of the defense authorization bill would be one means of bringing the issue before the full House.

In other developments yesterday related to the Walker case, federal prosecutors in Baltimore, responding to a flurry of defense motions, said in court papers that they had no objection to requests by John Walker and his son, Navy Seaman Michael Lance Walker, that they be tried separately. They suggested that John Walker be tried first.

The prosecution responses also indicated that John Walker made a statement to FBI agents shortly after his arrest. In their response to a defense motion to suppress any statements made by John Walker, prosecutors said Walker had been repeatedly advised of his rights against self-incrimination and told agents he did not wish to waive them, but that he made a statement when he initiated a conversation with an agent. They did not detail the contents of the statement or indicate whether it was incriminating.