Ferdinand E. Marcos, president of the Philippines and cagey investor in Manhattan real estate, hears many things. He hears both President Reagan and Congress saying he has to clean up his act. He hears the voice of the opposition, the mob in the streets and even, if he listens carefully, the thump, thump of small arms fire as communist guerrillas slowly take over his country. What he needs to hear, though, is the bang, bang of construction -- the United States building its military bases somewhere else.

Just where else, I leave to the respective military services. Some have suggested the Marianas. Others mention Singapore. The list of willing hosts is long. For a poor nation, a U.S. military base can be the functional equivelant of a not-so-modest oil strike. The two in the Philippines, for instance, annually pump some $300 million into that nation's economy.

But between the Subic Bay Naval Base and Clark Air Force Base, both within 50 miles or so of Manila, Marcos has the United States between the proverbial rock and a hard place. The conventional thinking is that the bases are essential to the United States, and so we have no choice but to come to terms with Marcos -- even if he steals the Feb. 7 elections.

Of course, there is more at stake in the Philippines than just military bases. The country is our former colony -- an English-speaking, mostly Christian country with whom we have had a close relationship. Should it fall to a communist insurgency, the consequences might not be as grave as some say, but they would hardly be beneficial to either American or, history suggests, Filipino interests. You don't have to be Cambodian to have a killing field.

Experts now talk about that possibility. A Senate report estimates that the Philippines has three years to "effect fundamental reforms," after which the communist New People's Army could be directing traffic in downtown Manila. At the moment, however, reform is nowhere in sight. Instead, corruption is rampant, the army demoralized, the judiciary ineffective and the economy going resolutely in the wrong direction -- "negative growth rate," in the dumbfounding jargon of economics. About the only thing booming is graft, but you have to know the First Family to get in on that.

What's a world power to do? To that question, many in Washington have their hands raised. Lean on Marcos to call elections. (He's complied.) Lean on him hard to make the elections clean. (Don't hold your breath.) Lean on him still more to reform the army, end corruption and clean up the judiciary. In short, make the man into something he has not been for some time -- a benevolent democrat.

But there is no real leaning on Marcos if down deep he is convinced that while the United States would love to see democracy restored, it would settle for secure military bases. Officially, the United States has told Marcos that the bases are "ancillary" to reform, but behind that official statement can be heard the low moan of anguish coming from the Pentagon. While it's probably true the military never met a base it didn't like, those in the Philippines are really beloved. Not only have they been around forever, but when it comes to location, they really are unique. It turns out only the Philippines is where the Philippines is.

But the bases are clearly doomed if the communists take over, and maybe doomed in any case. Corazon Aquino, widow of slain opposition leader Benigno S. Aquino Jr. and an opposition presidential candidate, says they have to go. Maybe this is just campaign talk, but the United States ought to look elsewhere anyway. At minimum, it would free us from total reliance on the Philippines. At maximum, it would show Marcos we don't need him as badly as he may think.

Maybe that would encourage Marcos to mend his ways. But even if the possible loss of the bases failed to do that, it would still free us from the tether that connects us to a corrupt regime. For once, we could be ahead of the wave -- free to denounce brutality and corruption, free to assert American values and not have the rhetoric of democracy co-opted by communists who cynically seduce the population with the sweet words of Jefferson and then govern according to the dictates of Lenin.

The way to show Marcos that we mean business is to start searching for alternative bases. For the good of the Philippines, the man needs the riot act read to him. It ought to sound like hammers striking nails.