WASHINGTON--The Carter Administration yesterday urged Congress to approve $1.5 billion in loan guarantees for the financially troubled Chrysler Corporation.

The new plan would double the $750 million guarantees previously supported by the administration.

Prospects Uncertain

Passage of the bill will be difficult, said Rep. William Moorhead (D-Pa.), chairman of the subcommittee considering the proposal.

Analysts believe that Chrysler would be forced into bankruptcy without larger loan guarantees. Treasury Secretary G. William Miller said yesterday. Chrysler is the nation's third largest automobile manufacturer.

Chrysler's collapse would "affect the stability of the nation's overall economic outlook" and might lead to substantial unemployment and economic disruption, Miller said.

No Better Ideas

"We need to maintain a competitive posture in the auto industry," added Miller. Chrysler's bankruptcy would leave only two major American auto manufacturers--Ford and General Motors.

Chrysler announced Tuesday it lost $460 million in the third quarter of this year, the largest deficit ever for an American corporation.

Problems of Philosophy

Although they disagree philosophically with the notion of direct government intervention in private enterprise, administration officials decided to go ahead with the loan plan--the largest ever for a U.S. corporation--because of the seriousness of Chrysler's predicament, Miller said.