On several occasions during the public hearings, members and staff of the congressional committees remarked about the extraordinary failure of many witnesses to remember key events involved in the investigation.

Rear Adm. Poindexter, whose memory was legendary among his fellow Navy officers, was perhaps the the most frequent user of the phrase, "I can't recall." Meese, McFarlane, North, and several of the CIA witnesses also often had trouble recalling major incidents in which they had participated.

Lt. Col. Earl, North's deputy at the NSC, an Annapolis graduate and former Rhodes scholar, repeatedly failed during his four private depositions to remember events unless they were covered by notes he had made when they occurred. Even then, Earl had trouble recalling what he meant by disconnected phrases he had written down. Meese too could not reconstruct events or meetings beyond the notes that were taken at the time by his assistants. In his testimony, Poindexter came right out and said it: "If you've got a memo, maybe I can remember it . . . ."

Memory lapses were particularly important in the congressional investigation because, as North, Poindexter, Earl, and Secord all testified, they had destroyed key documents relating to the matters under investigation.

Even when participants have recalled events and conversations, they have often been contradicted by other participants' recollections. A case in point is a brief meeting on Nov. 25 or 26 (the participants have conflicting memories) involving North, Earl and Craig Coy, another North deputy. North had just been fired and was visiting Earl and Coy in their offices to say goodbye. During that conversation, North told them the president had telephoned him soon after the announcement that he'd been dismissed.

Earl, whose memory often failed him on other points, clearly recalled this conversation. He even told the committees who stood where when it took place. He said North "confided that one of the things the president said in the phone call was that he, the president, recognized, or that it was important that he, the president, not know -- words to that effect. I don't have the exact quote."

Under questioning, Earl said he understood this to mean that the president was talking about the diversion, and had said that he "could not know as opposed to didn't know" about it. In other words, Earl said, the president was passing North a message "or that he was relaying that some people around {the president} were saying, had made the observations, that this thing you don't know about."

North testified that Earl had remembered their conversation incorrectly. The president had told him only that "I didn't know," North said.

With a discrepancy as important as that, the memory of the third party in the conversation took on added importance. But Coy couldn't remember.

"I've scoured my brain," Coy told the committees in his deposition, "trying to find the little brain cell in there that may have heard something like that, but I can't find it."

As for Earl's version, "That sounds too much like a Watergate-James Bond kind of thing," Coy said. "I think I would have recalled something like that, and it just didn't strike me as anything like that in the conversation."

The president did not testify to the congressional committees, but he too had memory problems in his sessions with the Tower special review board. At his first meeting with the board on Jan. 26, the president said "that sometime in August he approved the shipment of arms by Israel to Iran," according to the Tower report -- although he was unsure of the precise date.

On Feb. 11, after reviewing the matter with chief of staff Regan, the president told the board that "Regan had a firm recollection that the president had not authorized the August shipment in advance," according to the board report.

Nine days later, the president wrote former senator John G. Tower (R-Tex.), chairman of the panel:

"In trying to recall events that happened 18 months ago, I'm afraid that I let myself be influenced by others' recollections, not my own . . . . The only honest answer is to state that try as I might, I cannot recall anything whatsoever about whether I approved an Israeli sale in advance or whether I approved replenishment of Israeli stocks around August 1985. My answer therefore and the simple truth is, I don't remember -- period."

Staff researcher Michelle Hall contributed to this report.