The oddest duck now quacking in Washington is what Senate intelligence committee chairman David Durenberger calls "tion." It's what comes about when the supposedly secret American role somewhere has become glaringly apparent but has not been publicly acknowledged. Afghanistan and Nicaragua are familiar examples. From what President Reagan said the other day, Angola may be on the way to becoming another.

The president had come home from Geneva promising, to Congress, "to support the heroic efforts of those who fight for freedom." Why, then, he was asked the next day, does your secretary of state not support Jonas Savimbi's UNITA freedom fighters in Angola? "I'm glad you asked me that," said Reagan. "We all believe that a covert operation would be more useful to us and (would) have more chance of success right now than the overt proposal that has been made in the Congress."

Before you jump the president, consider that he was forced into the considerable indiscretion of publicly announcing a covert operation by the prior indiscretion of Congress in publicly taking up several proposals to give aid or arms to Jonas Savimbi -- proposals that involve a hostile act against a sitting government and which in other times would have been handled quietly by the CIA.

And before you jump Congress, consider that it is struggling with the consequences of a national decision made almost 10 years ago. Congress, seared by Vietnam and having no other restraint at hand, put the rude but effective leash of a public law (the Clark amendment) on a champing executive to halt its secret aid to the same Savimbi in 1976.

In the Carter years, presidential ambitions for covert action were modest and did not strain the readiness of a Democratic Congress to do the shadowy work for which the CIA is traditionally available. There was a match, more or less, of restraint.

Then Ronald Reagan was elected, promising to restore the CIA as a usable tool of American policy. And somehow a whole flock of the new Marxist regimes of the late 1970s found themselves challenged by anticommunist insurgencies calling for help from Ronald Reagan.

Congress was slow to react, but by last summer it was aboard programs meant one way or another to aid guerrillas in Nicaragua, Afghanistan, Cambodia and Angola: the "Reagan Doctrine." Between the president and Congress there was now a new match, more or less, of attack.

The wisdom of the policy is not everywhere granted. But what concerns me more today is the gap between the growing momentum of American-supported counter-insurgency programs and the feebleness of congressional capacities to keep an informed eye on them.

As long as the president's acts in support of counterrevolution remain presumed rather than admitted, he will probably have the diplomatic leeway he needs to avoid having to take open responsibility. The Soviets and others sponsor all kinds of subversive operations and pay a propaganda cost but not a serious political cost. There is no evident reason why the United States can't do the same.

But whether the domestic public will be as forgiving is not so assured. On both the left and the right I hear pained sounds of unhappiness with the current policy of pretend. It offends a common American sense of law, regularity and openness. Why not, some people say, take the running of wars out of the CIA, which should be left to intelligence gathering and analysis and which pays a heavy toll for being diverted? Why not put the running of wars under the Pentagon, whose natural business it is?

The Senate and House intelligence committees are now trying to stir the CIA both to think and to tell about covert action more systematically. The committees are also trying to beef up their own capacity to follow what is going on and to keep it within the bounds of congressional tolerance. To the extent that they succeed, however, they pull a wrap of secrecy back over a foaming area of public policy. To the extent that they fail, America's supposedly secret doings spill out into public view.

Oversight, which means intelligence committee oversight, works well when there is a policy consensus, Durenberger points out -- as in Afghanistan. When there isn't, the full Congress moves into the act, committee bipartisanship suffers, leaks occur and -- a special irony -- the public debate loses the full participation of intelligence committee members, who are briefed but locked up by their security oaths.

I can live with the messiness, if it means the president is being asked the hard questions. The embarrassments of disclosure seem to me easier to accept than the risks of unched executive initiative. But it sure is an odd way to do business.