The self-portrait of Rear Adm. John M. Poindexter, drawn in many hours of testimony, portrays a national security adviser given to numerous lapses of memory about vital matters in which he was involved, all of which bear directly on the believability of his testimony. From the first day to the fifth of his appearance before the Iran-contra committees, when pressed for specifics about a significant meeting or conversation, Poindexter most often replied, "I don't recall" and "I don't recollect."

A close reading of his testimony shows him admitting only to what is contained somewhere in an existing record, with just one exception. On the first day Poindexter volunteered that he had destroyed a sensitive "intelligence finding" signed by President Reagan because he feared it would cause political embarrassment if revealed. By Poindexter's own account, that document was destroyed in front of witnesses.

Otherwise, Poindexter insisted on a piece of paper before he would acknowledge any new information. As he said at one point, "if you've got a memo, maybe I can remember it."

On other occasions Poindexter conveyed the impression of answering a question without really answering it. For example, Rep. Edward P. Boland (D-Mass.) asked Poindexter yesterday whether he had known that his deputy, Marine Lt. Col. Oliver L. North, had used officials from the State and Defense departments and from the Central Intelligence Agency in a particular secret operation. Poindexter replied:

"I did not micromanage this operation. I don't think it's appropriate, and I didn't do it. And so, the precise knowledge that I have on that issue is not significant enough to give you a positive answer."

This picture of a remote, forgetful Poindexter is sharply at variance with the meticulous, painstaking, efficient, "incomparable" naval officer cited by his superiors in fitness reports as possessing "spectacular mental capacity" and a "photographic memory" and as someone who "retains fully, recalls accurately and evaluates with a keen sense of what is important -- and what isn't."

The contradictions between those Poindexters was apparent throughout his appearance before the Iran-contra committees. The confusion was sharply crystallized in one remarkable exchange yesterday between the admiral and Sen. Sam Nunn (D-Ga.).

At issue was a luncheon meeting between Poindexter and then-CIA Director William J. Casey on Saturday, Nov. 22. For Poindexter, that day came near the denouement of an intense and fateful sequence of events in the unfolding Iran arms sale story, setting up what Nunn said "must have been a very important and perhaps traumatic meeting between the two of you."

Nunn crisply ticked off the events that preceded the Casey luncheon: Three days before, the president had given misleading information about the arms deal in a nationally telecast news conference, in part after being briefed by Poindexter. Two days before, Poindexter, Casey, North, Attorney General Edwin Meese III and Justice Department aides had met to discuss Casey's upcoming private testimony on the deal before congressional intelligence panels -- testimony that contained a concocted "cover story" saying "oil-drilling equipment" instead of arms had been shipped to Iran. The day before, while Casey testified evasively on Capitol Hill, Poindexter met with the president and Meese, and Meese was authorized to begin his "fact-finding investigation" on the arms sales. Later that afternoon, after being informed by Meese that two aides were coming to his office to review pertinent documents, Poindexter destroyed the original presidential "finding" authorizing an arms-for-hostages transfer. Saturday morning, before meeting with Casey, Justice Department aides arrived to review Poindexter's records.

These events, which occurred one right after the other in an atmosphere of great tension, were all part of the dramatic unraveling of the Reagan administration's darkest secret. One would think Nov. 22 must have been among the most difficult and memorable days in Poindexter's career. (Three days later his resignation was accepted, and soon after he was in the hands of an attorney -- one who presumably suggested that Poindexter recall all that had happened in those tense November days.) Nunn asked the admiral: "What did you discuss at the luncheon?"

He replied: "About the only thing I can recall was Director Casey giving me a debrief of his meeting with the two intelligence committees the previous day, going over the questions that had been raised."

"You don't recall anything else?" Nunn asked.

"The only thing I can be positive of that there was no discussion of the transfer of funds to the contras," Poindexter answered.

"Well, why don't you tell us what you're not quite sure of but think that you can recall?"

Poindexter's answer was: "That's all I can recall."

Pressed further, he said he couldn't recall any discussion about destruction of documents about the original intelligence finding -- the one he had destroyed a day earlier -- though it was a document of special concern to Casey, who had first sent it to Poindexter to get the president's approval and signature. Poindexter said he could recall nothing being said about the diversion of arms sale funds to aid the Nicaraguan contras, though North testified Casey knew all about the diversion and had even seen a memo describing it. Poindexter said he could recall no discussion at lunch of a threat by financiers involved in the arms sales to expose the diversion to the contras, threats described in a memo Casey had shown to Poindexter.

Although both men eating their sandwiches were, in intelligence parlance, "witting" of all those facts and others involving the covert operations involving Iran and Nicaragua, Poindexter's account was that he can't recall them discussing any of them.

"It seems to me," Nunn said, "in the light of the circumstances that we've been over, and we both agree to the sequence of events, that this was an enormously important meeting with you and Director Casey. And yet, you seem to not recall anything about it except that you had sandwiches."

For five days, a memorable aspect of Poindexter's testimony had to do with his memory. Many committee members were left wondering, in the words of Rep. Ed Jenkins (D-Ga.), whether the admiral's account contained "at best, technical truth." Others shared Senate select committee Chairman Daniel K. Inouye's (D-Hawaii) "gnawing question that all of us have: Is he withholding any information from us at this moment?"

Sen. Warren B. Rudman (N.H.), ranking Republican on the Senate panel, told Poindexter during his testimony that he believed the admiral. Last night, after the former national security adviser's testimony ended, Rudman said: "I thought Adm. Poindexter's testimony was candid but astonishing. Many of the things he said, frankly, no one on the committee really buys or understands, but that's his testimony, and I guess that we'll have to live with it."

But even if its credibility was suspect, the testimony illuminated some aspects of the Iran-contra affair, especially this key participant's cast of mind. Poindexter's preoccuption with secrecy, his obsession with leaks, his immense contempt for and distrust of the news media and Congress, his repeated assertions of presidential supremacy in foreign policy, his stated belief that for himself and members of the National Security Council, "their only loyalty is to the president" -- all these were revealing of attitudes that contributed to the problems now confronting president and Congress.

For the American people, whose understanding and support Poindexter claimed to have, the question was both general and specific. Do they believe him when he said he didn't tell the president about the fund-diversion scheme because he wanted to give the president "deniability" -- and because he knew the president would have approved it if asked?

Or do they believe that his subordinate and fellow covert operator, Oliver North, was telling the truth when he recalled that he and Director Casey had discussed North's willingness to be the fall guy for the diversion and that Casey "did not think," in North's words, "that I was senior enough" to take the blame.

North was asked whether Casey suggested who was senior enough.

"He suggested that it might be Adm. Poindexter."