Washington — Some experts contend that the situation in the Philippines is unraveling, with President Ferdinand Marcos less and less in control. The resignation Monday of a five-member commission of inquiry into the assassination of opposition leader Benigno Aquino is seen by the experts as a blow to Mr. Marcos and one more sign that the command of events is slipping away from the Philippine president.
But other experts - those in the US government, in particular - argue that it is much too early to count the wily Marcos out.
Most observers of the Philippines here seem to agree that skillful American diplomacy could make the difference, some say, between the situation evolving toward more democracy or more violence.
One of Marcos's strengths has been to give the impression at least that he is one step ahead of events, always holding the initiative. But the evolution of the on-again-off-again commission of inquiry into the Aquino assassination has defied his control. An earlier commission chairman, Philippine Supreme Court Chief Justice Enrique Fernando, resigned when he was confronted with legal challenges to his impartiality. Marcos named a new chairman, Arturo Tolentino, a member of the national assembly from Marcos's ruling party. But Mr. Tolentino resigned on Monday, calling the commission a ''waste of time and money.'' The other commissioners followed suit, citing the public's lack of faith in the panel's impartiality. The latest reports from Manila indicated that Marcos was planning to name another panel to investigate Aquino's death.
Meanwhile, a Philippine government lawyer investigating the case said gunpowder burns were found on two security guards who escorted Aquino off the plane just before he was shot. The government had said Aquino's escorts were unarmed.
Many experts tend to agree that Marcos now faces the most serious threat to his rule since he imposed martial law 11 years ago. If he does not move carefully, they warn, he could polarize the situation, playing into the hands of left-wing extremists. Says one expert, who requests anonymity, ''The middle could drop out.''
''There is far more open opposition to Marcos in the city of Manila than ever before,'' says Carl Lande, a political scientist at the University of Kansas with long experience in the Philippines. ''Marcos certainly has the military force available to put the opposition down, but that would bring with it a further polarization.''
The important new element, Dr. Lande says, is growing opposition to Marcos from middle-class businessmen, who originally welcomed martial law. Lande and other academic experts tend to agree that the Reagan administration skillfully handled the postponement of President Reagan's trip to Manila, planned for early November. Some other experts now urge the US to strengthen ties with moderate opponents of Marcos and foster a succession excluding Marcos's wife and his military cronies.
''The entire political situation appears to be in an early stage of unraveling,'' says Peter Stanley, a historian who is dean of Carleton College in Northfield, Minn. ''The slow peeling off of supporters of Marcos that began a couple of years ago has greatly speeded up.''
Dr. Stanley says that the Reagan administration has gone a long way to distance itself from the Marcos regime and that this is proper. He does not anticipate the imminent fall of Marcos. But he asserts that in the long run ''it is hard to imagine that Marcos will be able to last and transmit his authority peacefully.''
''He will probably find himself so very much on the defensive that he will only be able to act with brute force,'' Stanley says. He argues that the US must help prepare the way for an orderly transition to democratic rule.
This is not going to be easy. Even while keeping lines out to the opposition, US officials must deal with the regime in power. The Reagan administration has limits beyond which it will not go in loosening ties with Marcos. Officials say that the Subic Bay Naval Base and Clark Air Force Base in the Philippines, the two largest American bases of their kinds outside the US, are invaluable assets.
But the administration has distanced itself to a degree from Marcos since the honeymoon period of mid-1981, when Vice-President George Bush, visiting Manila, declared, ''We love your adherence to democratic principles and practices.''
The US is urging the Marcos government to pursue a vigorous, impartial probe of Aquino's killing. The US ambassador in Manila attended Aquino's funeral, and more than once, US officials paid their respects to his family.
Testifying before Congress on Sept. 13, Deputy Assistant Secretary of State John C. Monjo described the assassination of opposition leader Benigno Aquino in Manila on Aug. 21 as ''a tragic event which has beclouded the reputation of the Philippine government.''
He said it is imperative that the Philippines parliamentary election next May be one in which the opposition has a free and fair opportunity to participate.