White House counselor Edwin Meese III spoke favorably yesterday of a proposal to change federal law so that defendants would be found "guilty but insane" rather than not guilty by virtue of insanity.

In a luncheon session with reporters Meese stopped short of giving formal administration endorsement to the proposal, but said the idea would be discussed with Senate Judiciary Committee Chairman Strom Thurmond (R-S.C.).

On Tuesday, the day after a federal court jury found John W. Hinckley Jr. not guilty by reason of insanity in the shooting of President Reagan and three others on March 30, 1981, Thurmond proposed speedy action on a pending bill that would require a defendant to prove insanity beyond a reasonable doubt.

Meese, an attorney, said the idea of creating a "guilty but insane" verdict was "a very good suggestion," and that the administration would make specific recommendations after discussions between Justice Department officials and members of Congress.

Administration officials want to work with the Judiciary Committee, Meese said, to change the present standards of criminal insanity in the wake of "the events of recent days."

"Whether you go to a concept of guilty but insane or have a uniform definition throughout the federal government and a uniform burden of proof, either one will be a major improvement in the law," Meese said.

He tried to avoid commenting directly on the verdict. But he predicted that the Hinckley case would become "a milestone" leading to revision of the insanity defense.

"The idea that the burden of proof is upon the prosecution to prove the defendant sane is an almost intolerable and insuperable burden," Meese said. "I was going to say you couldn't even prove this group the Washington Press Club sane. . . . I'll liken it to the White House staff. You couldn't even prove the White House staff sane beyond a reasonable doubt. It's a tremendous burden."