COL. NORTH yesterday presented as the ''ultimate irony'' and as a great trick played on Ayatollah Khomeini that Iranian money had ended up paying for the Nicaraguan resistance. There was a certain nodding of heads in the congressional hearing chamber, but this really cannot be allowed to stand. For it was precisely President Reagan's ill-fated attempt to buy back American hostages by sending arms to Iran that launched the fiasco now being unravelled on Capitol Hill.

True, a great trick was played. But it takes an extraordinary, almost willful blindness not to realize, especially at this late date, that it was played not by the clever, self-congratulating men in the Reagan administration but by none other than the Ayatollah Khomeini. The Americans are still tittering that some of his funds were diverted to the Nicaraguan contras. But the ayatollah has had himself the stuff of a belly laugh.

Recall that President Reagan had insisted he would not negotiate with terrorists and that he had organized an international arms embargo against Iran. Suddenly the United States is sending its emissaries to arrange the dispatch of extremely valuable American missiles for use in Iran's invasion of Iraq, whose support has become a principal American objective. The United States is even accepting the humiliating requirement of proving its good faith to Tehran.

The ayatollah lets one or two hostages dribble out but immediately sees to the replenishment of the supply -- new live hostages are quickly found and seized. Stunningly, he finds that even when he does not deliver up hostages, he still gets arms! And not only has he invented a kind of perpetual motion arms-supply machine. He has also taken a considerable political hostage: the story of the secret American dealings is his to divulge. The convulsions unleashed when he does divulge it are, of course, still in train.

Col. North is quite right when he declares that there is an ''ultimate irony'' here. But the real ''ultimate irony'' is that the American perpetrators of the Iranian gambit still do not realize that the United States was skinned. Imagine: the United States has been embarrassed in front of Arab moderates and European allies, its policy on terrorism has become a mockery, it has given palpable aid and comfort to a detested regime that is penetrating the territory of a friendly state, the Reagan presidency has been catapulted into unprecedented crisis, and Oliver North, a loyal soldier, sits before Congress and reports smugly that he and his undercover colleagues pulled off a brilliant coup.