Oliver L. North was on the offensive yesterday, and for much of an extraordinarily emotional Iran-contra hearing day proved to be the best lawyer in his own defense. It was his day in court, and the jurors that concerned him were not the members of Congress but the American people watching on television.

In the morning, he was combative and indignant as he sought to disprove charges that he had profited personally from Iran-contra deals. He evoked hearth and home, gave impassioned speeches in response to questions, and denied allegations that he had misused cash or traveler's checks for his and his family's benefit. "Not one penny, never ever," he said heatedly, his voice huskier than usual and sounding close to breaking as he responded to questions about death benefit funds set up for his family and about disbursing money from secret White House reserves for personal uses.

He did confess to making "the grossest misjudgment that I have made in my life" -- falsifying documents to hide his acceptance of a security system installed at his Virginia home and paid for with Iran arms sales proceeds. But this, he maintained, was done because he had been targeted for assassination by terrorist Abu Nidal and was unable to obtain government protection for himself and his family.

In one of the most remarkable moments of the day, North directly challenged Nidal to meet him mano-a-mano "on equal terms anywhere in the world." In fact, North was challenging the congressional committees head-on -- initially, with considerable success.

But as the day wore on, the tone of the hearings shifted. North's repeated assertions of absolute assurance and of always acting for a higher cause clearly began to wear on the committees. The day concluded with a stern catalog of North's actions in participating in lies to Congress and the public from chief counsel John W. Nields Jr. of the House select committee.

"As I understand your testimony," Nields said, "you and others put out a false version of facts relating to the 1985 Hawk {missile} shipment. You altered documents in official NSC files. You shredded documents shortly after you heard that representatives of the attorney general of the United States were coming to your office to review them. You wrote false and misleading letters to the Congress of the United States."

This was followed by an unusually strong rebuke from the normally taciturn Senate committee chairman Daniel K. Inouye (D -- Hawaii), who chastised North for suggesting that congressional committees cannot keep government secrets.

Viewers were left with a host of conflicting impressions about North the true believer and North the defender of personal honor and integrity.

At times his tactics sounded like Richard M. Nixon's famous Checkers speech of 35 years ago. Like North yesterday, Nixon then faced a moment of supreme crisis and public testing -- and all in the glare of the most intense public spotlight. Nixon's speech defending his acceptance of money from a so-called "slush fund" from wealthy contributors -- and refuting allegations that his wife received a mink coat -- was an attempt to salvage his place as Dwight D. Eisenhower's running mate in 1952. It attracted 58 million viewers, the largest TV audience to that time.

Nixon's references to his children and his wife's "Republican cloth coat" and his description of a gift of "a little black and white cocker spaniel named Checkers" drew sneers for its bathos. But the public responded favorably, saving his political career.

Though North's plight is different (he remains the target of a criminal investigation), he too seemed concerned with reclaiming his reputation, first by refuting allegations that he profited personally from the arms deals.

The security system, he explained with earnest, almost soulful demeanor, was a response to a death threat from Nidal. "I'll be glad to meet Abu Nidal on equal terms anywhere in the world. Okay? There's an even deal for him. But I am not willing to have my wife and my four children meet Abu Nidal or his organization on his terms," North testified.

And the traveler's check from contra funds that he cashed at Parklane Hosiery, a local shop? North said he asked his wife -- "my best friend" -- about this: had he ever been to that store? "You know what she told me? 'Of course you did, you old buffoon; you went there to buy leotards for our two little girls.'" Not a cloth coat, leotards.

Toward the end of the day, North told the committees that since he was fired from the NSC job nearly eight months ago, he has received about 50,000 letters. All but about 50 support him as a guy who tried, he said.

After his second day of testimony, North stopped briefly on the steps of the Russell Senate Office Building and spoke again to the television cameras about those letters. Keep them coming, he asked, appealing directly to the jury that seemed to count most to him yesterday, the American public.