In four days of testimony last week, Marine Lt. Col. Oliver L. North admitted previous lies to Congress, the attorney general, CIA officials, people who worked for him and representatives of Iran. But, he insisted, this time he was telling the truth about the Iran-contra affair.

Part of his testimony was backed up by documents. But other long passages were composed of assertions and assumptions, some unconfirmed, others already denied, about the knowledge and participation of his superiors.

When North and his personal magnetism vanish from television screens this week, he will have left a record that draws most of the key players in the Iran and contra operations more firmly into what he called "Ollie's dragnet," and outlines administration efforts to cover up the operations once the scandal broke.

North's testimony swept up the late CIA director William J. Casey, Secretary of State George P. Shultz, Attorney General Edwin Meese III, officials at the Defense Department, State Department and Central Intelligence Agency, and two previous bosses, former national security advisers John M. Poindexter and Robert C. McFarlane.

In four remarkable days, North placed Casey at the center of a closed circle within the government that secretly carried out military support for the contras when it was barred, diverted funds to the Nicaraguan rebels from proceeds of U.S. arms sales to Iran and, when the operation was discovered, systematically attempted to destroy all records and mislead Congress about what had happened.

If North's portrayal is accurate, Casey -- whom North described as a father figure -- could be remembered as one of the most deceptive Cabinet officers in modern times and as a man who may have irreparably damaged his friend, Ronald Reagan.

North also expressed admiration for Poindexter, saying he was "an admiral I would follow up any hill, anywhere." But his testimony also put Poindexter in a box. Next to Casey, North said, Poindexter was the individual most responsible for the activities now under investigation. He said that Poindexter, along with Casey, knew of, and by implication approved, North's destruction of records and preparation of false testimony to Congress.

If North's testimony is accurate, Poindexter misled North for 11 months about presidential approval of the diversion.

North told the panels that he went to Poindexter in January 1986 seeking specific presidential approval for the diversion idea. After telling North that "this had better never come out," Poindexter subsequently led North to believe that the project had the president's approval. But on Nov. 21, with the Iran-contra affair unraveling, Poindexter told him that the president did not know, North testified.

All that is damning testimony -- but only if it is true.

"North fantasizes and mixes things up as he always has," says a high-ranking U.S. official who worked closely with him over the past several years.

This official points out that North several times claimed that the CIA did not have a Farsi speaker able to serve as translator in the secret U.S.-Iran negotiations surrounding the arms sales, so North and his group had to turn to a retired CIA official provided by Casey. In fact, this official said, there were several Farsi speakers available, but none that North and others involved in the clandestine initiative would trust to participate in what the CIA bureaucracy considered a highly questionable operation.

Casey is not alive to refute any of North's assertions about his role. Neither is Vice Adm. Arthur S. Moreau, who North said had detailed knowledge of his activities in support of the contras in Central America, as well as of the diversion of funds from the U.S.-Iran arms sales.

Two living senior officials who were caught up in the "dragnet" last week, Meese and Shultz, vigorously challenged the accuracy of North's testimony through their spokesmen.

North initially said that Meese had knowledge of a controversial November 1985 Hawk shipment to Iran soon after it took place, and placed him in a room where North, Casey and others were preparing false testimony for Congress last Nov. 20. But North later retreated from that position after Meese's office issued a statement saying that the attorney general did not know the United States had participated in the shipment of weapons from Israel to Iran until a year later.

Pressed by House minority counsel George Van Cleve, North backed away from his earlier testimony and stated that he did "not recall addressing" the November 1985 shipment when he went to the Justice Department in January 1986 to review a presidential authorization for future transactions with Iran.

North told the investigative panels that Shultz had praised him as recently as last September for his "remarkable job" in "keeping the Nicaraguan resistance alive." A Shultz spokesman later confirmed that the secretary of state had made a congratulatory statement to North but said it referred only to his job in keeping up contra morale.

Denials aside, it remains to be proven one way or the other just how much Meese, Shultz and others named by North knew about or participated in the Iran-contra activities now under intense scrutiny.

When North's testimony about individuals has been related to specific documents, in particular the entries in his spiral notebooks, its accuracy has not been questioned. For example, North was asked to comment about a notebook entry referring to an April 25, 1986, meeting with Assistant Secretary of State Elliott Abrams, at a time when U.S. military aid to the contras was banned.

The entry included a reference to Blowpipe missiles, which North, according to other documents, was attempting to obtain for the contras from Britain. North said he could not recall the discussion but did not deny having talked about Blowpipes on that occasion. Abrams has not denied it, either.

North appeared to resist implicating Abrams, the CIA's Duane Clarridge and McFarlane, but at times he seemed to go out of his way to draw in other individuals or organizations. For example, when he was asked about whether he had passed CIA intelligence data to the contras to help them militarily, he volunteered that most of the intelligence he delivered was from the Defense Department -- one of the few major agencies to be relatively unscathed by the Iran-contra affair so far.

Sprinkled throughout the testimony were trivial embellishments of the facts. At one point, Senate counsel Arthur L. Liman joked that he was losing his eyesight from reading documents North thought he had shredded. Moments later, North offered the comment that he had "typed my fingers to the bone." Then he caught himself and said he meant his secretary had.

In some respects, North's most credible testimony concerned the activities and knowledge of the president. North said he had seen a signed intelligence finding covering the November 1985 transfer of U.S.-made arms from Israel to Iran in Poindexter's office.

Committee sources say it is unlikely that North would testify falsely on that under oath, because Poindexter is the next witness.

But North's memory failed him on other, more recent events.

North said repeatedly that he was unable to remember key details of what he said during the almost four hours he was interviewed by Meese. But he gave a flat denial to the question of whether Meese asked him to retain the documents in his NSC files.

He also could recall no details of a May 1986 National Security Planning Group meeting at which the president and top Cabinet officers discussed what they believed was the desperate need of the contras for money, which was North's main concern at the time.

Liman had to show North a document listing him as having attended the meeting before he would acknowledge he was present.