WASHINGTON--President Bush said yesterday that Panama's presidential election was marred by fraud and irregularities and called on military ruler Manuel Antonio Noriega to "heed the call of the people" and relinquish power.

White House press secretary Marlin Fitzwater said Bush was considering options ranging from military force to economic sanctions against Panama.

But the president said he would not talk about U.S. alternatives until Panama announces the official results of Sunday's election.

U.S. officials said privately that an invasion was highly unlikely and that more probable options would be to strengthen military forces, impose tougher sanctions or withdraw military dependents and civilians.

"I call on all foreign leaders to urge Gen. Noriega to honor the clear results of the election," Bush said in a hurriedly called question-and-answer session with reporters in the Oval Office.

"I would like to think that he [Noriega] will heed the call of the people and that he would listen to the international outcry that is building and that he would step down from office--in which case the relations with the United States would improve dramatically and instantly," Bush said.

Bush hopes that pressure from other Central American nations and the apparent success of Noriega's opposition will persuade him to abandon power, said an administration official, speaking on condition of anonymity. "We're going to proceed slowly, we're going to take our time," the official said.

The president commented after meeting with a delegation of official U.S. observers. In late afternoon, Bush met in the Oval Office with former President Carter, who led another observer delegation.

Afterward, Carter accused Noriega of "thievery" and said election tabulations he examined were "patently counterfeit." He called Noriega "amoral."

Standing in a light rain in the White House driveway, Carter cautioned against the use of U.S. military force and said the United States should not abrogate the Panama Canal treaties, which were negotiated and signed during his administration.

"Any sort of military involvement down there would immediately alienate the Panamanian people, who respect their nation's sovereignty as do we," Carter said. "And obviously unilateral action is much weaker than action in concert with other democratic countries. I think these are more fruitful."

As for abrogating the treaties, Carter said that would "play right into the hands of Noriega. It's the kind of thing he would like to see...It would alienate every other nation in this hemisphere."

Carter, who was accompanied by other members of his team, told Bush that a scientific poll conducted by the Roman Catholic Church with a maximum margin of error of eight or nine percent said Noriega had won in only two polling places.

Bush said the observers' reports "demonstrate clearly that despite massive irregularities at the polls, the opposition has won a clear-cut, overwhelming victory."

"The Panamanian people have spoken and I call on Gen. Noriega to respect the voice of the people and I call on all foreign leaders to urge Gen. Noriega to honor the clear results of the election," Bush said.

There were these other developments:

.The official U.S. delegation reported to Bush that, in the words of its chairperson, "We didn't see any way that it could be a free and fair election."

.Pentagon spokesperson Dan Howard said the Defense Department had alerted American military personnel stationed in Panama and their dependents to avoid travel around the country.

.The State Department contradicted a Panamanian government assessment that, based on returns from four of 40 election districts, Noriega's handpicked presidential candidate, Carlos Duque, was leading opposition candidate Guillermo Endara by 80,646 votes to 54,437.

Rather, said State Department spokesperson Richard Boucher, the administration believes Panamanians voted by margins of two or three to one to replace Noriega's regime.