FOR SEVERAL hours on Thursday morning, the House Republican loyalists on the Iran-Contra committee and their lone Senate brother, Orrin Hatch, thought they had died and gone to heaven.

At last, after six weeks of purgatory with assorted second-raters and shady operators telling lies, they had found a Moses in uniform, a Marine who was equal parts Booth Tarkington impish adolescent and James Bond fearless agent. Mary McGrory is a Washington Post columnist.

Oliver North, the cutest colonel the country ever saw, had transformed himself into the "national hero" of Ronald Reagan's original, derided designation. Capitol Hill was swamped with adulatory phone calls. The wonder worker turned the hearings on the scandal into the contra rally that true believers had always thought they could and should be.

His grin, his husky tenor, his quavering recital about being a terrorist target and a fall guy had the country on its knees and the committee on its back.

He did what other men dream of doing -- came home as late as can be to an uncomplaining wife, dashed off to Central America, to Paris, London, Frankfurt ("I can't remember which"), told off foreign ministers, whistled up planes -- although he couldn't, according to one of the few diminishing documents circulated in the jammed Senate Caucus Room, get rides in White House pool cars.

On Thursday, he did another Walter Mitty thing. He told off Congress right to its teeth. Members had prevented him from reading his opening statement at the outset -- he had, typically, ignored the rules for such submissions. They may have been sorry that they didn't get it over on the first day when he was not yet an idol of the airwaves. He has proved "ballistic" on camera.

Armored with public approval, he began, with the certitude that marks all his views and declarations, to judge his judges. North regards himself as a law unto himself, a trait shared with the former boss he still reveres -- the president who could pardon him should the independent counsel turn out to be unintimidated by television ratings.

"The hearings," he said in his soothing tones, "have caused serious damage to our national interests. Our adversaries laugh at us -- and our friends recoil in horror. . . . To hold them publicly for the world to see strikes me as very harmful."

The masochists among the president's loyalists sat back wearing the "lineaments of satisfied desire." They have flogged themselves for the congresssional failures he cited, a "fickle, vacillating, unpredictable, on-again, off-again policy towards the Nicaragun democratic resistance." They are patriots by his standards -- they support the contras. So indeed, does a majority of the 27-man combined committee.

But even sweeter moments were to come. Under the reverent questioning of Republican counsel George Van Cleve, a man of aggressive nondescriptness, "this kid," as North calls himself, gave the pro-contra pitch that during the dark days of the Boland Amendment opened a hundred right-wing wallets and bought arms and equipment for "the brave campesinos" that cause North's throat all but to close in admiration.

When he had finished, it seemed there was nothing to do but to close down the committees, approve the $105 million the president wants for the contras and tell Independent Counsel Lawrence Walsh, who has North under criminal investigation, to go jump in a lake.

It may take schoolteachers several generations to keep their pupils from aping North's lamentable grammar. The objective case is unknown to him. He says, "He told he and I. . . ." and once even, "Mr. Nir told he. . . . ."

It may take mothers even longer to cure their children of his one-size-fits-all alibi for lying. He admits he lied to his superiors, his associates and Congress. But he concludes with a defiant lift of the chin, "I lied to save lives."

No man has done more for sophistry.

No one on the committee interrupted. The one protest came came from the spectators. Two men stood up and unfurled a banner that nobody could read and started shouting, "Why not ask him about the non-combatants that have been killed?" and "What about the cocaine trade for the contras?"

They were hustled out. They were members of an organization called "The Emergency Response Network." During the commotion, North shook his head disapprovingly. It was a vulgar display of a lack of patriotism as he defines it, and a disruption of congressional proceedings much more direct than his.

The country is glommed onto the spectacle of a wizard showman turning the tables on his inquisitors. He has rescued himself from public opprobrium, and he could lift Reagan out of the mire on his magic cloak. Who could fail to admire a man who had the wit to hire such a prodigy?

One man can break the spell. It is, of course, the committee's Senate co-chairman, Daniel Inouye of Hawaii. He is a small man of great decorum and dignity. He has medals to match North's. He is a patriot who knows what democracy is all about.