President Carter's clemency program for Vietnam-era veterans expired last night, amid indications that Carter might go along with Congress and agree to strip veterans' benefits from some of the servicemen whose discharges were upgraded under his program.

Only a small minority of those eligible took part in the program Carter announced March 28 to fulfill a campaign promise.

According to Defense Department figures, 264,000 veterans with general discharges and 161,000 with undesirable discharges were eligible to ask that their discharges be upgraded.

Undesirable discharges are given for misconduct or security reasons, a Pentagon spokesman said, while general discharges are given for less than satisfactory performance of duty. Both tend to make it harder for a veteran to get jobs, studies have shown.

As of last week, 37,283, or about 9 per cent of those eligible, had applied. Some 62 per cent of them had undersirable discharges, a Pentagon spokesman said.

Those whose discharges were upgraded to general or honorable, a total of 16,227, according to Pentagon figures, are automatically eligible for veterans' benefits under present law.

But Congress sent the President a bill last week stripping veterans' benefits from all who had their discharges upgraded under Carter's clemency program and under an earlier one declared by President Ford, if they were absent without leave for 180 consecutive days or more.

The bill thus knocks out the automatic eligibility for benefits in current law, and orders the Defense Department to take a second look at each case, then decide on a case-by-case basis whether each veteran should be eligible.

At a news conference yesterday, the American Civil Liberties Union and the United Church of Christ urged Carter to veto the bill, and threatened a lawsuit if he doesn't.

David Addlestone, director of the ACLU's discharge review project, said the bill denies equal protection of the law to Vietnam-era veterans generally, as well as the poor and the uneducated who won't be able effectively to argue their cases or hire lawyers to represent them.

Carter said after his news conference last week that he hadn't made up his mind about the bill, which the Veterans, Administration opposed.

He said he could have signed the Senate version, which did not include the automatic stripping of benefits from those absent 180 days or more. But one administration source and another on Capitol Hill indicated yesterday Carter would not veto the measure, which passed both houses by overwhelming margins.

The President has until midnight Saturday to decide. If he does nothing by then, the bill will become law without his signature.