The Pentagon said yesterday that it planned to widen the use of lie detectors to combat espionage, while a law professor charged that the real objective is to intimidate defense employes who might give out embarrassing information.

"Although the proposed policy changes admittedly would permit a greater use of the polygraph within defense, the effect of these changes is neither as dramatic nor pervasive as one might believe from the press coverage," retired Army Gen. Richard G. Stilwell, deputy undersecretary of defense for policy, told the House Judiciary subcommittee on civil and constitutional rights.

Stilwell said "a substantial expansion" of the use of lie detectors "is likely to occur" only within those defense agencies doing intelligence work, conducting "sensitive" research or involved with operations requiring "compartmented" access, such as the Iranian rescue mission in 1980.

"We believe the polygraph can help us to ferret out those who might take the risk" of disclosing sensitive information to "a hostile government," Stilwell said.

He confirmed that the directive would empower Pentagon executives to ban people who refused to take lie detector tests from certain sensitive jobs and that employes holding "special" intelligence credentials would have to undergo such examinations to keep those clearances. He added that people with special intelligence clearances would be tested at random, probably with computers making the selections.

Outside of those special categories, people could refuse to take polygraphs without penalty, Stilwell said. "It is not our desire to clamp down on leakers" that motivated the directive authorizing wider use of lie detectors, Stilwell said; the aim is to provide "greater assurance" that defense employes in sensitive positions "are not spying for a hostile government."

Pentagon spokesman Henry E. Catto Jr. on Nov. 18 went beyond that scope, declaring that wider use of polygraphs was under consideration partly because "we want to discourage people with hidden agendas" from leaking information "outside the democratic process."

William H. Taft IV, Pentagon general counsel, said he is still reviewing the proposed polygraph directive and would probably suggest changes to safeguard further the privacy and civil rights of individuals to be covered.

Christopher H. Pyle, who teaches constitutional law at Mt. Holyoke College and has made a speciality of studying the use of polygraphs, said the draft directive suggests that "this administration is less interested in national security than it is in political security."

The proposed widened uses of polygraphs by the Pentagon "are part of a much larger policy involving efforts to classify more information, to restrict access to classified information, to restrict official contacts with the press and repeal the Freedom of Information Act."

He said the draft directive "pays lip service to the principle of volunteerism," permits "much more intrusive" interrogation than current rules permit, and allows personal information obtained through lie detector tests "to lie around forever" rather than be destroyed.