Panama's National Assembly voted to remove figurehead civilian President Eric Arturo Delvalle from office early this morning after he ordered the dismissal of the country's military strongman, Gen. Manuel Antonio Noriega.

In a 10-minute emergency meeting that was boycotted by opposition legislators, the assembly unanimously adopted a resolution ousting Delvalle and asking the Cabinet to name a new president, The Associated Press reported. The assembly said the president violated the constitution by "overstepping his powers" in trying to fire Noriega, United Press International reported.

Yesterday, in a taped, nationally broadcast radio address, Delvalle dismissed Noriega as head of the Panamanian Defense Forces, saying, "There is no other alternative but the use of the powers that the constitution gives me, to separate Gen. Noriega from his high command and to entrust the leadership of the institution to the current chief of staff, Col. Marcos Justines."

There was no comment during the day from Noriega, the de facto power behind the government, and Justines turned down the appointment.

Delvalle, reached at his residence by telephone from Washington last night, said that there were Defense Forces troops around his house, but they were clearing visitors and that there "had been no hostilities." He said Noriega had not communicated directly with him since he issued his order.

Delvalle said that he did not consider himself to be in any personal danger and that he believed the Defense Forces would respect him as constitutional commander-in-chief.

In the address, Delvalle said he had asked Noriega several days ago to step aside voluntarily pending an investigation of drug-traficking and other charges against him, but that Noriega had refused. He said he ordered Noriega's dismissal "to allow justice to continue an impartial course without pressures of any kind."

Delvalle emphasized in the telephone interview that he did not consider Noriega "guilty of anything" but believed that "a person that occupies such a high position should separate himself from that position so that he can be judged" fairly.

Earlier in the day, high-ranking officers told reporters in Panama that Noriega would defy Delvalle's order and said they backed him in doing so, Reuter reported. "None of us wants to be commander. Our commander is staying. The president is going. We all support Noriega," said Col. Leonidas Macias, military chief of police.

Justines said on military-run television last night that Delvalle had acted "under pressure from the United States. I think it was a grave error."

Delvalle told The Washington Post that he considered Justines' refusal to accept command of the Panama Defense Forces "the product of emotion and not good judgment in the situation that the country finds itself."

He said he believed that "all would be winners if the general {Noriega} accepted the situation and my proposal."

Late last night, the military command ordered the closing of the opposition daily La Prensa and a television station owned by Delvalle, The Associated Press reported, quoting employees.

U.S. officials said last night that while Delvalle obviously did not have the personal clout to enforce his orders, his move was a significant demonstration that the power base on which Noriega has depended for the past decade is eroding.

The question now, the U.S. officials added, is whether Noriega's opposition within Panama and abroad can exploit the situation to convince the Panamanian officer corps -- the ultimate source of Noriega's strength -- that the long-range interests of the Panama Defense Forces would best be served by forcing the general to step aside and permit elections for a democratic, civilian government.

The U.S. government, led by President Reagan and Secretary of State George P. Shultz, has been urging that course on the Panamanian military since popular discontent exploded into rioting last summer because of Panama's declining economy and charges that Noriega was involved in widespread corruption.

A White House statement issued last night by spokesman Marlin Fitzwater said:

"We understand that President Delvalle today dismissed Gen. Noriega from his position as commander of the Panama Defense Forces. At this time we want to reiterate our unqualified support for civilian constitutional rule in Panama. There is but one legitimate, sovereign authority in Panama and that is the Panamanian people exercising their democratic right to vote and elect their leadership in a free society."

Delvalle said from his home that U.S. Ambassador Arthur Davis, who visited him briefly last night, "supports, totally and absolutely, my decision" to order the Noriega's ouster.

A Pentagon spokeswoman said the U.S. Southern Command, the Panama-based headquarters for the U.S. military in Latin America, "is on normal status at the moment." She said that no alert had been ordered, although "they might be advising {personnel} to avoid demonstrations."

Panama, a country of 2 million people, is regarded as of major importance to U.S. national security interests because it is the site of the Panama Canal, the Southern Command and the principal banking and business center of the Central American-Caribbean region.

However, U.S. efforts to influence the situation there have been complicated by the action earlier this month of two federal grand juries in Florida that indicted Noriega on charges of involvement in international narcotics trafficking.

U.S. officials have said privately that the indictments -- a virtually unprecedented step against a foreign figure of Noriega's rank -- have greatly reduced their room for bargaining with him. They have said Noriega is convinced that if he surrenders power and leaves Panama, he would be treated as a pariah by other countries and would be hounded by efforts to get him to this country to stand trial.

With the potential for U.S. action at least temporarily circumscribed, the officials said that what happens next will be determined by events within Panama. There, they stressed, the key question will be whether Delvalle's action will precipitate further hemorrhaging of Noriega's internal support.

The general has sought to add to his military support by building a populist following among Panama's largely poor masses. He also derived considerable middle-class support from some segments of the business community and the large government bureaucracy dependent on his political patronage.

U.S. officials cautioned that there are no signs of major cracks in the military's support, but they noted that if the military finds the gulf widening between it and the rest of the country, there is certain to be greater questioning within the officer corps about the wisdom of continued loyalty to Noriega.

The officials predicted that Noriega's opposition will seek to capitalize on the situation by appealing to Latin America's democratic governments to call for a return to civilian rule in Panama. Gabriel Lewis, a former Panamanian ambassador to the United States who has been living here since last summer helping to organize exile opposition, sounded that theme last night by calling Delvalle's move "a very courageous act."

In San Jose, Costa Rica, Ricardo Arias Calderon, the principal opposition leader and head of the Christian Democratic Party, said he had been ejected from Panama when he and his wife, Teresita, tried to return to the country from Miami yesterday, Washington Post correspondent Julia Preston reported.

He said he was dragged across the airport by security men and put aboard a flight for Costa Rica when he tried to enter the country.

"Obviously they have expelled me from Panama in violation of our constitution. What we have is an honest-to-goodness de facto regime run by an honest-to-goodness thug, a criminal," he said, referring to Noriega.