Considered as a painting, the hostage episode, if hung in the gallery of contemporary politics, would be a miniature. But it is not less a masterpiece for its scale, considering the exquisite delicacy of draftsmanship by the terrorists.

This episode -- surely not a "crisis," considering the good feeling all around, once the murder was forgotten -- passed smoothly from the cake- and-Pepsi leave-taking party in Beirut, on to the Damascus Sheraton. There, tributes to just about everybody (including the terrorists, but not including President Reagan) floated out over flowers that were a genteel touch at the last press conference. This was, we are assured, a genteel terrorist episode except, of course, for the matter of the Navy diver. At the press conference, several hostages said it had b a heck of a "learning experience" in which they had learned about our common humanity, etc.

A "senior official" of the U.S. government explained, at the quiet end, that "vengeance" is not our style. Our style had been displayed when a "senior official" said: "We figure that (Israel's Prime Minister) Peres can read our minds. . . . Certainly there are enough people over here of the Jewish faith . . . who must be telling people over there (in Israel), 'For God's sake, look what you're doing to (American) public opinion.'

The U.S. government's mind was indeed an open book. Its policy was an evenhandedness too scrupulous to notice distinctions (as between America's enemies and allies; between kidnapping and military detentions): Everyone should release everyone held "illegally." U.S. policy proclaimed the symmetry, the proportionality, the equivalence of terrorists kidnapping Americans and Israel detaining persons -- all protected by Israeli law -- who menaced Israel's withdrawal from Lebanon into Israel's northern settlements.

The terrorists were dealing from a stacked deck the Reagan administration had helped stack. A crucial card in their hand was dealt many weeks before the episode began. It was dealt by the State Department declaration that Israel's detention of those people violates the Geneva Convention. Assume for a moment that the State Department's opinion -- gratuitous, mean-spirited and probably wrong -- is right. All it involves is a technical offense: Israel's detention of the Shiites would have been "legal" if Israel had detained them a few miles north of, rather than south of, the Lebanese border.

The terrorists' goals almost certainly included more than the already promised release of the detainees. The goals, now achieved, probably included demonstrating the emptiness of U.S. rhetoric about terrorism (retaliation, and all that), and driving a wedge between the United States and its only ally in the Middle East. The terrorists also achieved this bonus: the president praised the anti-terrorism of the Syrian regime that was responsible, with one truck bomb, for the bloodiest day the Marine Corps has suffered since Iwo Jima.

The brutalized and murdered Navy man was not buried before the hostages' captors had found among the hostages an energetic collaborator, Allyn Conwell. An oil man who makes his living selling things in the Middle East, he was not content with serving as a megaphone for the terrorists and a tutor to the world on the fine points of Israel's failings under international law. When the president demanded the release of the seven Americans who were taken as hostages long before Conwell was, Conwell criticized showing such inconvenient concern for too many Americans.

Then, Monday morning, just when you thought it was safe to turn the television back on, there was the irrepressible Phyllis George saying Conwell would make a splendid candidate for public office. Senator from Oman?

Things came out Conwell's way: the other seven are still hostages. The U.S. government had used the word "insist" in demanding the release of the seven but, then, it had said it would not ask Israel to cave in to terrorists and then -- see paragraph three, above -- incited American Jews to do just that.

The administration denies that it pledged not to retaliate. It says it will now build on the heightened public concern about terrorism. But the president, sitting in the Oval Office, sanitized the Syrian regime, which his administration says practices state-sponsored terrorism of the sort that blew U.S. forces into retreat from Lebanon.

There is no reason to think that that regime will abandon such a successful and risk-free tactic. There is every reason to think that the president's praise for Syria, a Soviet client, has immunized it against any retaliation for the terrorism sequels it probably will help sponsor.

This time, as every time, U.S. policy regarding retaliation is: "Next time. . . ." This policy is diplomatic Tupperware, cheap and durable and reusable. It has to be, because it is used in all the terrorism episodes it incites.