The Philippine crisis bedeviling the United States presents the threat of a geopolitical catastrophe in the Far East for which American diplomacy has no ready antidote.

The Reagan administration, haunted by the prospect of an Iranian-style diplomatic debacle, is debating whether to keep prodding President Ferdinand Marcos to make substantial reforms, or to begin distancing the United States from him in hopes of preserving the U.S. position in the Philippines for the long term.

The debate inside the administration is strongly influenced by intelligence reports that Marcos is gravely ill and probably has no better than a 50 percent chance of living until the next Philippine elections, scheduled for 1987.

For now, the United States is relying on diplomatic persuasion, epitomized by the recent mission of Sen. Paul Laxalt (R-Nev.) to Manila in an effort to persuade Marcos to mend his ways before his country collapses beneath a growing communist insurgency.

But this is a temporizing tactic. The main unresolved issue, officials say, is whether to continue trying to nudge, cajole and squeeze Marcos toward meaningful reforms or to give up on him. The latter course would, in effect, aid noncommunist domestic opponents trying to oust Marcos in favor of a government that could more effectively fight the growing communist insurgency on the island republic.

The debate within the administration is mirrored in Congress, where views are just as divided, mostly along partisan lines. Rep. Gerald B. Solomon (R-N.Y.), a close friend of Marcos, argues that abandoning Marcos could provoke what his critics say they are trying to avoid for the United States.

"We have to be very careful about pulling the rug out from under Marcos," he said. "We tried to do it in Iran with the shah on human rights. Had we been a little more patient with the shah, maybe we wouldn't have the same situation we have today in Iran."

Many Democrats, on the other hand, argue that the time has come for a dramatic break with Marcos and the administration's tactic of "quiet diplomacy," because "the negative trends are moving faster than the positive ones," as Rep. Dave McCurdy (D-Okla.), a member of the House Select Committee on Intelligence, puts it.

"Gradualism isn't going to work. We have to look at reasonable, constructive alternatives to the Marcos regime -- a moderate, noncommunist regime," he said.

Marcos suffers from an often incurable, recurring sickness known as "systemic lupus erythematosus," according to intelligence and congressional sources. The disease affects the cell structure of the body and attacks organs, particularly the kidneys. Marcos has survived three debilitating bouts, the latest from November to March. He may have had a kidney transplant, although he has vehemently denied it.

Each time, Marcos has recovered -- but each time to "a lower plateau," according to one U.S. official. During his "downs," he is almost incapacitated, said the official, who asserted that Marcos is "hardly able to operate his government."

A congressional source who has investigated Marcos' health said the Philippine leader has virtually destroyed his presidency as a functioning institution and has taken to ruling mainly by "capricious decree." This source said Marcos may die within six months.

"The best course for U.S. policy is to let nature take its course," the source said.

To what degree Marcos' illness is the driving concern behind the Reagan administration's sudden activism toward the Philippines is unclear. There also have been recent U.S. intelligence reports that the spreading communist insurgency, led by the New People's Army, is leading the country steadily toward "catastrophe."

The nightmare frightening administration policymakers is the possibility of a strategic reversal in the balance of power in the Pacific if the United States loses its two biggest bases abroad, Clark Air Force Base and Subic Bay Naval Base, both in the Philippines, and the Soviet Union takes them over -- precisely the fate of the former U.S. base at Cam Ranh Bay in Vietnam.

Calls for the United States to get out of Clark and Subic are coming from noncommunist quarters in the Philippines as well as from the communist insurgents. U.S. officials fear that the bases will become identified with Marcos, making it all but impossible for any successor government in the Philippines, even an anticommunist one, to allow the United States to keep them after Marcos is gone.

Parallels between Marcos and the late shah of Iran haunt this administration debate. "Everybody has a fear of Iran and what it did to the Carter administration," said one administration official. "It may not go the way Iran went, but it could go just as sour."

The Carter administration tried to deny it had a problem in Iran until both the shah and the U.S. position in Iran were too far gone to salvage. That experience has had a powerful impact on the Reagan administration, which openly acknowledged long in advance of the denouement that it has a potential foreign policy disaster on its hands.

"The Philippines has been on the president's horizon ever since 1983," said one official, referring to the murder of opposition leader Benigno S. Aquino on Aug. 21 of that year, an event that set off the first alarms in the White House and led to a Reagan refusal to meet with Marcos ever since.

U.S. foreign policy analysts in and out of the administration agree that the U.S. dilemma today over how to handle Marcos differs in many ways from the Carter administration's Iranian problem.

Marcos' position in Philippine history and society is different from what the shah's was in Iran. Internal conditions of the two countries are also vastly different, and there is no Philippine equivalent of the Islamic fundamentalism that stirred the Iranian masses.

But there do seem to be three clear similarities.

Both countries were, at the moment of crisis, crucial to U.S. geopolitical interests in a key region of the globe. And Marcos demonstrates a stubborn refusal to appreciate the seriousness of his situation similar to the shah's -- a stubbornness that hardens whenever Marcos is pressed to make reforms that risk loosening his tight grip on power.

The Marcos message that "all is under control" was repeated to Laxalt last week in Manila. Marcos reportedly asked whether his regime had "an image problem" in the United States, and needed a good public relations firm in Washington to set things right.

This same message was brought to Washington this week by his acting foreign minister, Pacifico A. Castro, who said in an interview Monday, "We are doing all the reforms necessary and called for by our people."

U.S. "experts" misperceived what was unfolding in South Vietnam, Cambodia and Laos, Castro said, suggesting that the same misperception is affecting U.S. policy in the Philippines. "It could be we are going through the same syndrome," he said.

A third similarity between the cases is the terminal illness of the leader. The Carter administration, however, did not realize that the shah suffered from serious cancer. According to Gary Sick, the National Security Council expert on Iran during the Carter administration, the misbegotten belief that the shah was in good health was important to the administration's decision to keep supporting him.

"We know Marcos is going to pass on in a relatively short time. The question is how to position yourself. That is the real difference that affects the whole underlying philosophy of how you deal with the situation," Sick said.

Another difference between the two cases, according to Sick, is the initial responses of the two administrations to their respective crises. During the past year, he noted, there has been a steady stream of high-ranking U.S. officials and members of Congress to Manila bringing messages of deep concern or even blunt statements of U.S. displeasure with Marcos' performance.

Not so in U.S. dealings with the shah. As late as November 1978, just three months before his final flight from Tehran, President Jimmy Carter's national security affairs adviser, Zbigniew Brzezinski, was telephoning the shah, encouraging him "to toughen up" his stand against the opposition with the assurance that "we are prepared to back you whatever you do," according to Sick.

The effectiveness of the Reagan administration's full-court diplomatic press on Marcos is unclear. Everyone seems to agree some reforms are taking place, But, as one U.S. official involved in the process said, "It's a struggle every step of the way."

Some administration analysts say they feel that there is a "reasonable chance" of achieving the current U.S. goal of free and fair local elec- tions next May, to be followed by a presidential contest in 1987 when a Philippine vice president also will be chosen. Others are dis- tinctly gloomy about such poli- tical prospects.

As one administration official put it, "We can't make major pro- gress before a new government is in place."