UNITED NATIONS -- A day of poking around produces the quiet but satisfying discovery that ''the United Nations'' is, if not making progress in ending the Iran-Iraq war, then putting the effort to good Soviet-American use.

I say ''the United Nations'' because although its working chamber -- the Security Council -- has no formal existence and mandate outside the will of its members, there nonetheless is an unmistakable chemical entity that consists of those members, the secretariat and the atmosphere that emanates from the always-stunning glass tower and from the enduring sensible part of the United Nations idea.

By the latter I mean not that countries will bring their sovereign national interests to heel for the sake of an abstract idea of international amity but simply that they will see if those interests can be fairly served by using the forums and ways of the world body.

Ronald Reagan and Mikhail Gorbachev have not abandoned skirmishing for political and strategic advantage in the Gulf, but the deeper current is their quest for the benefits of working together.

Reagan in effect is trading in the old Western monopoly in the Gulf -- a position that was slipping badly anyway -- for a joint reach for regional stability. Gorbachev is accepting the uses of American power (he doesn't ask for the withdrawal of the U.S. Navy until there's a cease-fire) in order to head off the specter of a victorious rampant Islamic Iran.

In the code of the Soviet foreign minister: ''it is extremely important to preserve unity in the Security Council.'' Why so? To make sure that Iran and Iraq, especially Iran, accept the council's July 20 resolution calling for a cease-fire and settlement. The one-country-one-vote General Assembly is anarchy. But the U.N. Charter endows the select council -- and especially its five veto-wielding permanent members -- with extensive powers, and it is these that the Russians now seek to apply.

The United States agrees. Our man, Gen. Vernon Walters, is trying to pin the Kremlin down to an arms embargo against Iran if Iran continues to dance around the July 20 resolution. To keep the Soviets in harness, he agreed to risk letting a vote on an embargo slip for a few days. They wanted to give the secretary general time for a bit more diplomatic exploring.

We should see soon whether it was worth the wait. Meanwhile, evidence of Soviet-American cooperation accumulates. Secretary General Javier Perez de Cuellar had discovered that where Iraq wanted the July 20 resolution put into effect sequentially (a cease-fire is the first item, a commission to inquire into the origin of the war is the sixth), Iran wanted to make an undeclared cease-fire and the commission's establishment simultaneous first steps. Last Friday he went back to the council and asked for further instructions. The council told him to nail down a formal cease-fire.

The two powers are looking hard at that commission. The original idea was to satisfy Iran's bitter and justified complaint that, as Iran's president told the General Assembly, when Iraq invaded in 1980 the council ''did neither mention any aggression or occupation nor make a request for returning to international borders but, astonishingly enough, called on both parties not to resort to force any further.''

The Americans and, one can infer, the Soviets see the difficulties of setting up an inquiry from which Iran and Iraq demand diametrically opposed results. But at a minimum the exercise would allow Iran the political and psychological satisfactions of airing a profoundly felt grievance. That Iran sees identification of the aggressor as a quick, first political task and determination of the consequences as a second, slower judicial process may indicate its priorities.

All this does not mean it is now a sure thing that Iran will accept the council's diplomatic demands or buckle under to a later arms embargo. The prudent expectation is that Iran will twist and maneuver and fight on through at least one more big fall ground offensive.

It does mean that Moscow has been ready to work publicly with Washington, to forgo a gaping opportunity for scoring points with Iran and to prevent Iran from playing the two great powers off against each other. Reagan has done his part. The United Nations is stage and producer of this rare experiment in regional cooperation, whose implications extend beyond whatever immediate results it may bring in the Gulf.