The Reagan administration added to the pressures on Philippine President Ferdinand Marcos yesterday by endorsing statements by his opponents in his most serious internal crisis.

A White House statement, issued in mid-afternoon after a conference call between President Reagan and his senior foreign policy advisers, quoted approvingly from statements by Philippine Defense Minister Juan Ponce Enrile and acting Chief of Staff Lt. Gen. Fidel Ramos justifying their break with Marcos and saying that "the mandate of the people does not belong to the regime."

"These statements strongly reinforce our concerns that the recent presidential elections were marred by fraud, perpetrated overwhelmingly by the ruling party, so extreme as to undermine the credibility and legitimacy of the election and impair the capacity of the government of the Philippines to cope with a growing insurgency and a troubled economy," said the White House statement, issued by spokesman Larry Speakes.

The United States supports "resolution of the issues involved by all the people of the Philippines as quickly as possible" and "expects" this to be done without violence, the White House statement said.

The statement, which ignored Marcos' charges of an assassination plot against him, seemed to move the administration further toward the opposition camp at a crucial moment.

Moreover, the Pentagon has agreed to take opposition leader Corazon Aquino aboard a U.S. ship near Cebu if she is threatened with harm, according to Sen. John Melcher (D-Mont.). The State Department said no request for refuge had been made by last evening.

In a novel twist to a power struggle in a foreign country, ABC News announced that Enrile is to be interviewed from his heavily guarded military headquarters today on "This Week With David Brinkley" if he is physically able to participate. On the same television program last Nov. 3, Marcos first made public his intention to call an early presidential election rather than waiting until his term is up in 1987, and the U.S. news media have played an unusually important role in the Philippines events and the U.S. response to them.

Marcos' failure to win a broadly accepted mandate in those elections, in which there was widespread disenfrancisement, intimidation and fraud decried by Congress and eventually by the Reagan adminstration, led to the current crisis.

High stakes for the United States are at risk in the Philippines, including nearly a century of close connections, large-scale U.S. investments and two of the most important military facilities available to U.S. naval and air forces in Asia.

The possibility of devastating violence if Marcos decides to confront his challengers by force was among the most pressing concerns of the administration, officials said. But in view of the U.S. shift away from Marcos since the Feb. 7 elections, there was doubt in official circles whether the United States could wield effective and immediate influence.

Rep. Stephen J. Solarz (D-N.Y.), chairman of the House Foreign Affairs subcommittee on Asian and Pacific affairs, criticized the White House statement as too vague and indirect. "At this point we need to say very clearly we think Marcos should resign. With the fate of the Philippines in the balance, this is the only way to avoid massive bloodshed and even civil war," he said.

Solarz, an outspoken critic of Marcos, urged the administration to offer Marcos safe haven in the United States if he steps down peacefully. This position was endorsed by Rep. Jim Leach (R-Iowa), senior Republican on the House subcommittee. Solarz and Leach and other members of their subcommittee voted unanimously Thursday to cut off direct military aid to the Marcos regime, arguing that it had lost its legitimacy because of the election frauds.

Sen. Sam Nunn (D-Ga.) said Reagan should offer Marcos asylum "if he steps down peacefully and if he does so immediately and if he does so without bloodshed."

Sen. Richard G. Lugar (R-Ind.), chairman of the Senate Foreign Relations Committee and cochairman of the U.S. observer group that monitored the recent Philippine election, suggested that Marcos should resign, saying, "He may decide to hang on for a period of time, but I think it's rapidly approaching the time when he must make some decisions on behalf of peace and stability in the Philippine islands."

A senior U.S. official said that as of late yesterday afternoon the administration had not weighed in with diplomatic messages to either side in the Manila standoff, but that this might be done soon.

Enrile telephoned U.S. Ambassador to the Philippines Stephen Bosworth minutes before announcing in a military headquarters news conference that he would no longer accept Marcos' authority, according to Washington officials. Bosworth spoke to Marcos by telephone about an hour later, but the Philippine president maintained he knew little or nothing about what was going on, the sources said.

Enrile and Ramos reportedly launched their action after a meeting about 3 p.m. yesterday, Manila time, about an hour after special White House emissary Philip C. Habib had left the Philippines following a week of fact-finding. According to Washington sources, Enrile told Ramos at that time that he had received information that they were about to be arrested and suggested that they move quickly to protect themselves and rally others to the anti-Marcos cause.

Habib had seen both Enrile and Ramos, as well as Marcos and opposition leader Aquino, during his mission to Manila, according to the State Department. There was no indication, however, that the U.S. envoy learned in advance that a military crisis was about to break out.

Habib arrived earler than expected late Saturday night at Andrews Air Force Base, the White House said, and is to report "promptly" to Reagan. Habib originally was to stop overnight in Los Angeles. Before the latest developments, Habib was expected to meet Reagan Tuesday morning.

The White House statement yesterday was drafted by Secretary of State George P. Shultz, White House national security affairs adviser John M. Poindexter and his deputy, Donald R. Fortier, and Undersecretary of State Michael H. Armacost, according to White House officials.

Shultz then joined Poindexter, White House chief of staff Donald T. Regan and Secretary of Defense Caspar W. Weinberger in a 15-minute conference call with Reagan, who was at the presidential retreat at Camp David, Md.

The planned appearance of Enrile on the Brinkley show, which has also invited Marcos, caps remarkably heavy coverage by the U.S. media of the Philippine developments. The heavy coverage, especially television, contributed to strong public and political pressures on the Reagan administration to condemn the election as fraudulent and distance the United States from Marcos.

Since the beginning of the year, according to the Philippine Embassy, Marcos has appeared on ABC's Brinkley program, "Good Morning America" and "Nightline," CBS' "Face the Nation" and "Morning News," NBC's "Meet the Press" and "Today" programs, Public Television's "MacNeil-Lehrer NewsHour," John McLaughlin's "One on One" and Cable News' "Crossfire."

In the past four weeks, according to Issues Management, a Washington-area newsletter that measures output of the news media, about 180 minutes of Philippine news, the equivalent of three full hours, has appeared on the evening news programs of ABC, CBS and NBC. This coverage, second only to the space shuttle disaster in recent weeks, compares with an average of less than three stories per year on the television evening news on the Philippines in 1972 to 1981.