Contrary to the nearly universal belief in Washington, Jimmy Carter never was given any assurance before his approval of the U.N. Commission of Inquiry that this concession would lead to release of American hostages in Tehran.

That stunning disclosure was made last weekend by a top presidential adviser to influential Democratic senators. It spells out the sense of desperation in the Carter administration over resolving the hostage question. President Carter was merely planting a seed of hope for quick release of the hostages without commitment of any kind from the chaotic Iranian government.

In the view of those briefed on the true state of affairs, this points to a crescendo of new humiliations of the United States. It suggests that the revolutionary government in Tehran has set a course designed to toy with the United States mercilessly by dangling one "solution" after another, then withdrawing them with demands for sweetened U.S. concessions.

Carter's approval of the U.N. commission, coinciding with his campaign against Sen. Edward Kennedy in the New Hampshire primary, raised suspicions. But staunchest supporters in Congress assumed he had the equivalent of a signed agreement in his hip pocket. None of these Democarts thought for a moment that the president would rely on the good will of a revolutionary movement that does not conceal its hatred for him or his nation.

These Democrats could not be more wrong. For whatever reasons, Carter embarked on what may prove to be a costly fool's errand. Desperation for an end to the impasse led him to put his trust in Aytollah Khomeini and the keepers of Tehran's embassy jail.

The slow crumbling of unshakable U.S. positions, leading to one humbling concession after another, suggests that in the end Khomeini and the terrorists may obtain most of what they have always demanded. This at least includes "self-criticism" by Jimmy Carter of the past U.S. role in Iran.

But the Iranians want far more than presidential "self-criticism" for his country's "sins." They still want the shah, and nobody can any longer be sure they will not get him.

The U.N. commission will generate world publicity about alleged torture victims of the shah and other sins laid at his doorstep. That may well turn this country against the shah. "They're going to drag the shah down in the mud and work for a change in American public opinion," one senator told us after learning the truth from the White House.

That Carter would lend himself to such dangerous exploitation shows how far the U.S. position has receded from those early days last fall. National security adviser Zbigniew Brzezinski then was riding daily herd on the hostage crisis, using the Special Coordination Committee of the National Security Council.

This body was expanded during the early part of the hostage crisis to include Carter's two most initimate advisers: White House chief of staff Hamilton Jordan and press secretary Jody Powell. Jordan and Powell quickly became partisans of Brzezinski's no-concessions policy. Jordan had a personal hand in helping Brzezinski guide the SCC -- and the president -- toward a policy that established "national honor" as more important than the lives of the Americans held hostage.

But one internal development in Iran after another passed without hoped-for reward. Brzeinski's daily sessions of the SCC gave way to business as usual. The State Department here and U.S. diplomats at the United Nations exerted more influence as political tension on the hostages issue dimmed slightly and the Soviet invasion of Afghanistan commanded the SCC's full attention.

With Kennedy trying to salvage his fading campaign by exploiting the hostage issue, Carter on Feb. 13 announced his surprise approval of the long-considered U.N. commission.

Carter's three-month-old policy of no investigating commission before the hostages were set free was reversed in these words: "We would support steps by the United Nations that would lead to release of the hostages . . ." That deflated Kennedy's call in New Hampshire for a commission.

But checkmating Teddy surely cannot be the real reason the president bought a pig in a poke. He did so because he had no other options, and that is a working definition of despair.