American observers of Philippine politics were quick to draw dire, but often contradictory, conclusions from the murder of Benigno Aquino Jr. on a Manila tarmac this week.

Inconceivable, said some, that President Reagan should now visit and break bread with President Marcos on his November Asian journey. Inconceivable, said others, that he shouldn't. For the rest of us, it looks very much like another muddle in which the right course is less than starkly clear. And that is far from unusual in the troubled history of U.S.- Philippine relations.

Aquino, the most eminent of Marcos' many eminent foes, was shot dead as he stepped from his plane after a three-year U.S. exile. Clad in a bullet-proof vest, fatalistic about the end he suffered, Aquino was in government custody. You have to be pretty naive not to suspect foul play. Yet Americans, of all people, know how random assassinations can be.

Aquino's place in Philippine politics was not without ambiguity. But unless his record and utterances are extraordinarily deceitful he was a Jeffersonian democrat, challenging Marcos to live up to the democratic tradition he has thwarted for nearly 15 years. In him the "July 4" tradition ran deep and strong.

The act of having him shot at the airport seems, on the face of it, a bit too brazen for Marcos. He has treated Aquino (who used to be accused by the extreme left of being Marcos' stooge) with an odd mixture of vindictiveness and solicitude. He had him tried and condemned to death on dubious charges, then commuted the sentence, then imprisoned him, then freed him to undergo heart surgery in Texas.

Aquino was an idealistic democrat, surer than many that the values of freedom are the best antidote to Philippine fragmentation. The Philippines have been in one state of siege or insurgency after another throughout the 85-odd years of the American connection--from Aguinaldo in 1899 to the Muslims of the south islands today.

The care of the Philippine connection from our end has always demanded a certain juggling of interests and values. American investment there is substantial and boomed even after Marcos overthrew the constitution in 1972. Clark Field and Subic Bay remain the anchors of what remains, after Vietnam, of U.S. military power in Southeast Asia.

Accordingly, recent presidents have found it advisable to react mildly to the pleas of Marcos' critics and, indeed, to the occasional insolence of Marcos and his wife, Imelda ("minister of human ecology"). He has overthrown Philippine constitutionalism; he has flirted intermittently with such unsavory characters as Libya's Qaddafi; and he is constantly blackmailing the United States for higher rent payments for the military bases.

The Carter administration tried the artful straddle, coupling slight cuts in aid, and human rights pressure, with concessions on the status of the bases.

Its successors, rather typically, muted the human rights agitation and took a let-sleeping-dogs-lie approach. Far from distancing itself from Marcos, it actually congratulated him (in the words of Vice President Bush) on his "dedication to democratic principles." Certainly, more could be said of the principles than of the practice.

In partial defense of all this timidity, it was fashionable, four years ago, to worry that Marcos might crash as disastrously as the shah in Iran--with similar consequences for U.S. fortunes and interests.

The fear was probably exaggerated. The Philippines, overwhelmingly Roman Catholic, seem unlikely prey for a seizure of zealous clerical fundamentalism. But no president, even in the face of Marcos' foolishness, has ventured to say anything that might jeopardize the military leases. Sleeping dogs have been left to lie.

It is, of course, a familiar tale in the annals of American foreign policy, and to some degree--given that we cannot always pick or control our clients--inevitable. But the Aquino assassination, whoever is responsible, is a reminder that deference to dictators can be risky as well as demeaning.

The leases on U.S. bases will have to be renegotiated in less than a decade. Marcos is neither perpetual nor immortal. It is time to pay more attention to the grievances of his opponents, sharpened as they now will be by a cruel martyrdom.