Not since Gen. Douglas MacArthur's return to the United States in 1951 after he was fired by President Harry S Truman for insubordination during the Korean war has a military officer had such dramatic effect on the nation as Lt. Col. Oliver L. North.

For five days of emotionally draining and revealing testimony, North's personality, performance, tactics, values, beliefs and actions have been examined and cross-examined -- in the hearing room on Capitol Hill and by ordinary Americans all over the country. North took his case to the public beyond the hearing room and, in what amounted to a series of compelling speeches, clearly helped his own cause, portraying himself as a loyal subordinate following what he believed to be the lawful instructions of his superiors.

North's powerful impact on the investigating committees and the country is reflected in all the opinion polls and in the extraordinary range of general public reaction stirred by his appearances. As just one example, an ABC News Poll reports that 92 percent of the public thinks North did a good job in defending his actions, and 64 percent believes him to be a victim instead of the villain in the scandal.

The drama was distracting, as Sen. William S. Cohen (R-Maine) suggested. But Cohen added:

"Long after the sheer force of your personality has faded from this room, and that may be a very long time indeed, and long after these cameras that are here today are clicked off, I think the American people are going to be left to deal with the policy implications of what has occurred and what's been said in this room."

Where the country will finally strike a balance between North's formidable persona and the unpopular policies he helped to execute remains to be seen. Yesterday's hearings, marked by fundamental constitutional questions about the accountability of covert operations and by rancorous political rhetoric, demonstrated how difficult making that assessment will be.

At the witness table, North has helped himself principally in two ways. He openly admitted that he had lied to "unwitting" Reagan administration officials, misled Congress and the public, falsified and destroyed official documents as part of a preconceived cover-up plan designed to protect his superiors, and specifically the president. But he also implicated higher-ups with his repeated assertions that all of his actions had been approved by higher authority.

There's no mystery about North's public transformation. He remained silent, asserting his Fifth Amendment right against self-incrimination, and refused to testify for nearly eight months after the scandal erupted last November. Daily news reports brought fresh and seemingly damaging disclosures about the extraordinary range of his secret activities. Leaks from the Reagan administration enriched the portrait of North as principal miscreant in the affair -- a rogue operator carrying out his own secret war to the detriment of president and country.

Last week North finally got to tell his story. Instead of the evil duplicitous Rasputin of the Reagan administration, the country saw and heard a young, slim, appealing and articulate officer, medals for valor borne bravely across his chest, speaking with what seemed the utmost sincerity before an immense national audience.

At a time when the nation has been battered with tales of lying and cheating from Wall Street to the pulpits of famous preachers -- with those accused usually denying all -- here was a young American who admitted many errors. He was not the rogue of reputation; he was willing to take the blame for his deeds, he said. But he was not willing to take it all -- and he gave a devastating indictment of others above him. That self-portrait of an attractive officer seemingly abandoned worked powerfully with the public.

How effectively North made that case is shown by the polls reversing previous doubts about him. At the same time, according to the same surveys, the public believes that in his testimony North has been covering up for higher administration officials -- a belief held by 57 percent, according to ABC, as opposed to 37 percent who disagree.

Behind these figures lies the central contradiction in North's self-portrait as presented to the Iran-contra committees and the people through television: How can his professed expressions of honor and truthfulness be reconciled with his own admissions of lying in a higher purpose?

Throughout his first five days on the stand, North's tactic was to present himself as completely open and desirous of telling what he said several times was the "whole truth -- the good, the bad, and the ugly."

Yet his testimony has been marked by numerous lapses of memory in response to critical questions. These have included repeated statements about his inability to recall or recollect specific conversations or missing documents or incidents potentially damaging to him.

North has rationalized his actions, and often provided the committees with vague recollections about actions in which he participated. This line of response included his assertions that all his actions had been authorized by higher authority.

Questions about that claim were raised yesterday by several members, most sharply by House Majority Leader Thomas S. Foley (D-Wash.).

Foley directly asked North about his statements on receiving authorization, and North deflected the question. He also gave testimony conflicting with the recollections of his one-time National Security Council boss, Robert C. McFarlane.

The committees also have shown increasing readiness to challenge another of North's assertions -- that, as he testified repeatedly, he had lied in order to save lives that could be endangered if there were any leaks about the covert operations in which he was engaged. That, North has maintained, was one of the principal reasons for hiding secret operations from Congress.

Responding to that assertion, which has angered numerous members of the congressional committees, Cohen yesterday established that in fact Congress has been informed secretly of other covert operations during the Reagan years, "even when lives were at stake . . . and there were larger sums of money in those particular covert operations even than what we're dealing with with the contras and certainly the sale of weapons to the Iranians."

North agreed.

"So the notion that somehow when lives are at stake Congress cannot and has not been trusted is not the correct impression," Cohen remarked.

The committees and the public are confronted with two other factors that complicate any net assessment of North. One is the portrait of what might be called "the other Ollie" that emerges from the stacks of documents made public by the committees -- a different figure than the North whose demeanor and straightforward appearance have convinced many Americans of his truthfulness.

The documents refer repeatedly to the necessity for "stealth," for deniability, for cover stories, for hiding facts, for not stating the truth. The documents recount how North lied to Iranians, Israelis, the Federal Bureau of Investigation, the Central Intelligence Agency, the Justice Department, the attorney general.

One small note was revealing of a more general attitude. It is a passage in a private message from North to his NSC boss, Rear Adm. John M. Poindexter.

Said North:

"I agree that we cannot trust anyone in this game."

Have we been seeing another manifestation of the cynicism that animated that remark in North's testimony over the last week? Or can North's repeated protestations that he is now telling the truth be accepted at face value?

Another area is even more difficult to judge -- but it, too, has been made clearer during his testimony. It concerns personal values and the code of conduct North said he has followed since he was a midshipman at the Naval Academy in Annapolis.

Included in the record of North's congressional appearance is a copy of the midshipman's "honor concept," a code of conduct to be "a way of life rather than a set of regulations." Its first principles are: "a member of the brigade does not lie, cheat or steal."

Among the principles it defines are these: "Mislead or deceive: a deliberate misrepresentation of a true situation by being untruthful or withholding or omitting or subtly wording information in such a way as to leave an erroneous or false impression of the known true situation."

Yesterday, Oliver North heard himself praised as a patriot and hero, and defended by members of the House and Senate who said he should not be subjected to prosecution for his actions. Rep. Henry J. Hyde (R-Ill.) described North as "representing the old morality."

On that point, the jury is still out on Oliver L. North, the most compelling and perhaps most confounding witness of the generation.