The arrival of Fawn Hall at the hearings of the House and Senate select committees investigating the Iran-contra scandal occasioned near-hysterical excitement. Photographers vibrated with expectation; security men pounded up and down the halls bawling instructions to make straight her way.

A pretty, appealing witness was desperately needed. The morning and first hour of the afternoon had been spent in truly surpassing tedium, as an elderly 35-year-old named Bretton G. Sciaroni ground through his explanation of how he came to render a legal opinion that the Boland Amendment, forbidding military aid to the contras, did not apply to the National Security Council. He had a rather hangdog manner, and his second-rateness as a lawyer was inescapable to all but the most fanatical House Republicans. He was, despite his feeble credentials, the $62,000-a year counsel to what must be laughingly called the Intelligence Oversight Board.

A kind of gloom settled over the hearing room as the thought took root that there would be no Fawn Hall to redeem the day.

But the members finally showed mercy and forbore to question Sciaroni further. As the clock stood at three, Fawn Hall, on a wave of security men and photographers, gracefully entered the chamber, bringing the hearings their most admirable facial contours.

She is as slim as a reed, and her blond hair falls in crimped waves to her shoulders. She held her chin high as her training as a model had taught her and showed off her clean jawline. Her eyes are large and blue and her mascara is as dark as Tammy Faye Bakker's, although not so thick. She smiled without showing her teeth, while the cameras shoved and shouted "Fawn, over here" and "Fawn, how do you feel?"

Preceding her to the stand has been a depressing file of pirates, flag-wavers, liars and hustlers. She was the first one you wouldn't mind being at a picnic with. Felix Rodriguez had also been sincere, but he was an ex-CIA man, a member of the Che Guevara assassination team, and although he seemed to have some conscience, he was not a man you would feel easy about asking to pass the pickles.

Hall has a pleasant low voice, and she has been quizzed so often that she has mastered the witness skill of short answers and saying "correct" where indicated. She didn't natter, and she didn't seem to be pushing any particular vision -- or revision -- of herself and her activities. She repeated whenever possible her faith in, and admiration of, her boss, referred to properly as "Colonel North."

To Lt. Col. Oliver L. North, who was hurling planes, troops and ships around several continents, raising arms and money, she must have been a companionable, restful presence, and just about the ideal secretary. Not only was she fair to look upon, she had a policy, she said, of "not asking questions" and "doing what I was told."

She seemed to be the type who wouldn't mind getting coffee, either. She didn't mind running out into 17th Street to get packages of money from general Richard V. Secord's secretary when the occasion warranted.

She worked long hours without complaint. She believed in what North was doing. When it came shredding time, she had to keep her wits. She had to type changes in documents, return them to the files and make sure the originals were destroyed.

On Nov. 21, four days before the attorney general's earthquake news conference about the diversion of the Iranian arms money, life in the NSC got hairy. She took her place at the shredding machine by North's side, without question, and called the right person in the Crisis Management Department when the shredder jammed. It was not her fault that she was interrupted in the delicate business -- she did not say why -- which is, of course, the reason that enlarged originals are hanging on the walls of the House Foreign Relations Committee room and Hall is posing for dozens of sweating photographers, instead of one Frenchman shooting her for a layout in Glamour magazine on "Power Secretaries in the Nation's Capitol."

She did, she admitted under Senate staffer Mark A. Belnick's neutral questioning, feel "uneasy" and "uncomfortable" at certain stages of more blatant changes, like reducing a three-page memorandum about sinking, seizing or publishing the presence of, a munitions ship headed for Nicaragua. But she believed in North. When he told her on Nov. 25 that he had been fired, she said she burst into tears.

She was the first person to be granted immunity by independent counsel Lawrence E. Walsh. It speaks well of her intelligence that she accepted it in return for her story, which is by far the most riveting yet to be told.