President Reagan, reversing a strongly held position, issued a predawn statement yesterday urging Philippine President Ferdinand Marcos to surrender power and saying that "attempts to prolong the life of the present regime by violence are futile."

Reagan authorized the change in policy after the administration received word overnight of a possible attack by forces loyal to Marcos against the headquarters of breakaway forces headed by former defense minister Juan Ponce Enrile and Fidel Ramos, former acting chief of staff of the armed forces.

Officials said Reagan's message was conveyed to Marcos through U.S. Ambassador Stephen Bosworth. A source familiar with the situation said that Marcos refused to leave, but that additional discussions are being held in hopes of changing his mind.

Presidential envoy Philip C. Habib left Washington late yesterday for Honolulu. While a spokesman said his itinerary beyond that was "indefinite," the move would put him only a few hours from the Philippines in case sudden developments required his presence there.

Habib is one of the few people who has held extensive discussions in recent days with figures on all sides of the Philippines struggle and thus could play a pivotal role in arranging a transfer of power. Another possible mission for Habib would be to establish close U.S. relations with a successor government after a transfer of power, sources said.

A senior administration official said plans were being drawn to take Marcos out of the Philippines, either by flying him out of the country on a U.S. aircraft or meeting him at a rendezvous point after he flies out on his own plane.

The key problem remains that Marcos seems determined not to leave and is not yet convinced that his situation is untenable, according to an administration official.

Another official, who asked not to be quoted by name, said reports of Marcos' adamant insistence that he will not give up power seem to suggest he is losing touch with reality. "It's all over for him and it really has been over for days. The key questions are: Will there be more violence? And is Marcos going to be able to get out?" this official said.

On the latter point he said it is increasingly evident that Marcos' ability to move from the presidential palace in Manila has been impaired by the changing loyalities of the Philippine armed forces.

Habib, who returned from the Philippines only three days ago, and Secretary of State George P. Shultz went to Capitol Hill yesterday afternoon to brief key lawmakers on the rapidly changing situation.

Sen. Richard G. Lugar, chairman of the Senate Foreign Relations Committee and cochairman of the U.S. observer delegation which monitored the Feb. 7 Philippine elections, said after the briefing that the administration is engaged in "a delicate situation of negotiations" with Marcos.

Attending the meeting were 18 senators and nine House members, including members with foreign policy responsibility. Those in the meeting "expressed bipartisan support for a policy" of trying to avoid bloodshed in working with the opposition military forces, Lugar said.

Lugar said he has "come to the conclusion that the [Philippine] military has decided to back [opposition leader Corazon] Aquino and will be subservient to her control."

Sen. Patrick J. Leahy (D-Vt.), ranking minority member of the Senate Select Committee on Intelligence, said Shultz and Habib had expressed "a far more realistic attitude" than the administration had expressed earlier.

"The question is only when, not if, Marcos is going to leave," Leahy said. "Because of a long relationship with him, the United States is in a position where if he were to ask . . . for amnesty or asylum here, he would get it," Leahy said.

Provision of U.S. aid "is contingent on the manner of his leaving," Leahy said. "There is agreement [among congressional leaders] that if he leaves with a lot of bloodshed, that he's not going to be welcome in the United States under any conditions."

Expressing much the same sentiment, Senate Majority Leader Robert J. Dole (R-Kan.) said Marcos should be granted refuge in the United States only if he goes relatively quietly. "If he tries to hang on and creates a lot of problems and violence, I wouldn't be too anxious" to have him come here, Dole said. On the other hand, Marcos "would be favorably received . . . if a lot of people are not shot up."

Administration officials said reports of an impending attack received here early yesterday morning were sufficiently alarming that White House chief of staff Donald T. Regan and White House national security affairs adviser John M. Poindexter telephoned Reagan at 5 a.m. to obtain his authorization for an immediate public appeal to forestall violence and to encourage Marcos' resignation.

Until recent days Reagan had been a strong defender of Marcos. Even after sharply criticizing extensive fraud in the election, the White House said the political future of the Philippines was up to the Filipino people rather than the United States. As of late as Sunday afternoon White House spokesman Larry Speakes said it was "not our prerogative" as outsiders to ask Marcos to step down.

Speakes continued to call Marcos "an old friend and longtime ally." But he also said that in view of the possibility of serious violence in Manila, "we thought it was important we issue a strong statement."

The early morning White House statement did not explicitly appeal to Marcos to resign but made that point in roundabout fashion by saying, "A solution to this crisis can only be achieved through a peaceful transition to a new government."

Speakes told reporters, "As far as President Marcos leaving the Philippines, this would be a decision he would have to make."

Five officials of the Philippine embassy here issued a statement expressing solidarity with the opposition and calling on Marcos "to effect a peaceful transition" to a new government. Consulates in Los Angeles, San Francisco, Honolulu, Chicago and Houston -- and in London and Toronto -- also urged Marcos to step aside.

Philippine embassies in West Germany, the Netherlands and Belgium issued statements backing Aquino and calling for Marcos' resignation, while Filipino diplomats in Rome pledged allegience "to the duly constituted and recognized government." Asked who that was, a spokesman said only that "we shall have another statement tomorrow."

In Paris, the Philippine Embassy said Filipinos should "rally to the present overwhelming desire for change."