Now the President Reagan is established as a might figure in the Washington firmament and is evidently preparing to turn more from domestic to foreign pursuits, it seems the right moment to tell a little secret about the doubts expressed about is stewardship of international affairs.

It is this: few of the critics have their whole hearts in it. At the core of most of their complaints and grumbles about Reagan is a sneaking suspicion, often verging on a hope, that the old boy may come through after all.

One part of it is the reluctance to take on a president who has been a smashing success in what he has tackled at home and who has managed to story out of deep soup abroad, too. Another part is the apparently genuine patience and good humor with which the president and most of his chief aides have deflected or absorbed what criticism has come their way.

But some other currents are running. Everyone understands that the political techniques and resources governing domestic performance are not automatically exportable. In particular, Reagan cannot hope to reach out to foreign public opinion, over the heads of foreign leaders, the way he reached out to domestic opinion and thereby forced a reluctant Congress to go along with his economic program. a

It cannot hurt in foreign affairs, however, to be and to be regarded as a leader on the rise. Especially is this so in the many aspects of policy that entail a showing of control over one's own home political forces -- to ratify a treaty, to carry a budget, to make the bureaucracy responsive or to win time or room for a negotiating initiative.

It is not simply that Reagan is invulnerable to torpedoes from his right. It think he is better off in foreign affairs for having started at his own pace, for having had a domestic success in the meantime, and for not having committed himself where his previous stand was too vague or doctrinaire to be a good guide.

He is not, after all, a president fleeing to foreign policy in order to gain the stage for presidential action and achievement denied him by the supposedly intractable nature of our domestic political concerns.

You might even say this is potentially his finest hour: his domestic prestige is at a peak, his program has not had the time to flop, and his desired image of strength and toughness has not been seriously tarnished.

True, he does not have a national security David Stockman, a trusted and expert adviser who has already thought through the president's premises and who can show him precisely what he must do to achieve his goals.

Just at this moment, however, fate has handed him a nice opportunity to demonstrate the quality that is potentially far and away his most useful international asset. The opportunity is the air controllers strike and the quality is credibility. To the foreign affairs pros, who surely all are watching, the strike is no big deal, but Reagan's collapse under pressure would be. In his 200 days in office, he has had no better opportunity to show whether he is as good as his word in a bargaining crunch.

Hanging tough is not an unalloyed virtue. But here a closer look at the strike is instructive. The president is standing firm behind a legal, reasonable, principled position; that is why he is supported by public opinion. If he picks his foreign policy positions as carefully, he can expect the same strong support.

Many of his critics suggest he can be effective in foreign policy to the extent that he retreats from ideology to "pragmatism." I am often put off by the Reagan dogma, but it seems to be somewhat unrealistic, not to say patronizing, to expect him to back away from his basic beliefs."

Rather, I would look for him to produce some new combinations and definitions. In respect to the deep cuts he says he wants in strategic arms, for instance, it will be interesting to see if Reagan finally makes the show offer his rhetoric sometimes signals or an offer the Soviets find negotiable. Will he accept that the best way to blunt a Soviet push in the Middle East is to do what is necessary to ease the Israeli-Palestinian dispute? Is he not in a position to persuade the South Africans to contemplate risks in Namibia they might otherwise scorn?

Previous policies were not so effective as to make it self-evident that Reagan's way is a blind alley. This awareness dulls the critics' edge and inclines them, if not to cheer, to pull their punches and wait and see.