Lt. Col. Oliver L. North, ending seven months of silence, testified yesterday that he believed he had presidential authority to divert Iran arms sales proceeds to the Nicaraguan contras and had written five memos last year requesting President Reagan's approval for the funding scheme.

But during six hours of testimony before a packed Senate Caucus Room and a national television audience, North also told the House and Senate select committees investigating the Iran-contra affair that he had never discussed the diversion with Reagan nor seen any documents reflecting the president's authorization.

North's account of the five memos written beginning in February 1986, including three in which the diversion plan was outlined as part of a broader arms-for-hostages initiative with Tehran, provided a surprise opening disclosure from a witness whose appearance on Capitol Hill had been as eagerly awaited as any in memory. Only one memo, apparently overlooked when North systematically shredded evidence of the Iran and contra operations last fall, had previously been disclosed after it was discovered in North's files by Justice Department officials last November.

Contrary to his presumption that Reagan knew and approved of the covert financing of the contras, North testified, he was told last Nov. 21 by national security adviser John M. Poindexter that the president did not know. Four days later, after North had been fired from his National Security Council staff post, Reagan called him and "said to me words to the effect that, 'I just didn't know,' " North added.

While raising new questions for the White House about the diversion, North appeared to push the president more deeply into another aspect of the scandal by asserting that he had seen Reagan's signature on a key document that is currently missing.

The document, a presidential authorization for the Central Intelligence Agency to assist in a November 1985 transfer of arms by Israel to Iran, bluntly characterized the operation as an attempt to trade arms for American hostages being held in Lebanon, a description the president subsequently has rejected repeatedly.

North, who arrived at the hearings yesterday as the larger-than-life mystery man widely portrayed as the engineer of the intricate Iran-contra operations, sparred through much of the day with a stern House chief counsel, John W. Nields Jr. North also occasionally vented anger at those whom he said had tried to portray him as a "lone wolf" who was running covert foreign policy by himself.

"I don't want you to think, counsel, that I went about this all on my own. I realized, there's a lot of folks around that think there's a loose cannon on the gundeck of state at the NSC. That wasn't what I heard while I worked there. I've only heard it since I left. People used to walk up to me and tell me what a great job I was doing," North told Nields.

The drama began a few minutes after 9 a.m., when the thin, uniformed Marine officer with a chest full of medals was sworn in by Sen. Daniel K. Inouye (D-Hawaii), chairman of the Senate select committee, who had lost his right arm in World War II combat. For the occasion, Inouye had pinned on his Distinguished Service Cross.

But for a few electric moments, it almost seemed that North would not tell his story. Inouye read a letter received Monday night from North's attorney, Brendan V. Sullivan Jr., complaining that there had been insufficient time to examine the documents provided by the investigators.

But it quickly became clear that the committee was in no mood for making concessions to the reluctant witness. Noting that it was Sullivan who had requested to have North testify sooner than originally planned, Inouye declared, "If {Sullivan} is having troubles it is not because of our doings."

Inouye, who repeatedly overruled Sullivan's objections during the hearing, also denied a Sullivan request that North be permitted to make an opening statement. Inouye, who cited committee rules requiring that 20 copies of such a statement be filed 48 hours in advance, added, "Here once again the witness is asking us to bend the law and to suggest he may be above the law." Sullivan frowned but made no further move; North will be permitted to give his statement Thursday morning, after the required wait of 48 hours.

Yesterday's appearance was the beginning of what was supposed to be four days of testimony by North. But congressional investigators said they now believe the testimony will spill into next week before North gives way to Poindexter. Despite his many hours at the witness table yesterday, North barely scratched the surface of many of the complex and intriguing events underlying the Iran and contra operations during the past several years.

The former NSC aide also displayed a penchant for wisecracks and wry asides, commenting at one point that "the only thing that we did was divert money out of {Iranian middleman Manucher} Ghorbanifar's pocket and put it to better use."

Because of legal maneuvering that had prevented the two select committees from questioning North extensively in private before his public appearance yesterday, some investigators had openly expressed concern that in the setting of a televised, spontaneous hearing room, North would turn the inquiry into a forum on behalf of the contras and covert operations.

Instead, Nields reined him in when North began to make such appeals and often left the lieutenant colonel responding with quips.

"My memory has been shredded," North replied during one exchange about the shredding of documents at the NSC that is currently the subject of an obstruction of justice investigation by independent counsel Lawrence E. Walsh.

The repeated theme of North's testimony was that he operated only on the basis of higher authorization. Of the diversion of funds to the contras fighting the government of Nicaragua, he said: "I had the approval of my superiors, as I did for all the other things I did."

At another point he said, "I never carried out a single act, not one, Mr. Nields, in which I did not have authority from my superiors. I haven't in the 23 years that I have been in the uniformed services of the United States of America ever violated an order, not one."

Early in his testimony he declared: "I came here to tell the truth -- the good, the bad and the ugly." But he quickly added that he would not accept responsibility for that which he had not done.

The most striking example of that reluctance to shoulder the blame alone occurred in his unprompted disclosure that last October it was then-CIA Director William J. Casey who, with North, agreed to start destroying documents relating to the secret Iran-contra operations.

"Director Casey and I had a lengthy discussion about the fact that this whole thing was coming unraveled and that things ought to be cleaned up and I started cleaning things up," North said.

He implicated his friend and former boss, Robert C. McFarlane, more deeply in last November's effort to rewrite the chronologies of the Iran-contra affair to protect Reagan. Prodded by Nields, North said that McFarlane prepared what he knew to be "intentionally misleading" substitutions in the initial version and then "persuaded" North to insert them in the White House document that was being circulated.

North's list of people who knew that the document was wrong included his boss at the time, then-Vice Adm. Poindexter, and Attorney General Edwin Meese III. Earlier in the hearings, retired Air Force major general Richard V. Secord charged that the attorney general had betrayed North and himself last November when he publicly disclosed the discovery of the diversion.

Yesterday, North said he had a "general recollection" that Meese was aware of the November 1985 Israeli arms shipment around the time it occurred and that the attorney general hid that knowledge a year later when the White House was attempting to conceal Reagan's involvement.

A spokesman for Meese denied that assertion yesterday, saying that the attorney general did not know about the 1985 transfers of U.S. arms from Israel to Iran until Nov. 22, 1986, when former CIA general counsel Stanley Sporkin advised Meese about it during his fact-finding project.

Sen. Warren B. Rudman (R-N.H.), vice chairman of the Senate investigative panel, also said yesterday that the committees have material in hand that contradicts North's statements about Meese.

North repeatedly resisted implicating a friend and former associate, CIA official Duane Clarridge, who had handled the CIA's participation in the November 1985 shipment by Israel to Iran of Hawk antiaircraft missiles. Clarridge, in a sworn statement to the congressional investigators recently made public, said he believed the cargo was oil drilling equipment and did not learn the true contents until early 1986.

North stated at one point that he initially "lied" to the CIA about the cargo. But when pressed by Nields, North admitted that he had told Clarridge the cargo was Hawks as early as Nov. 25, 1985, less than 48 hours after the delivery.

North also expanded the number of administration officials who were aware of his activities on behalf of the contras during the 1984-86 period when U.S. military aid was restricted by the Boland Amendment.

He reported that he described these activities to the Restricted Interagency Group (RIG). The RIG was headed by Assistant Secretary of State Elliott Abrams and the CIA's Alan Fiers. Fiers, North said, had "an adequate sense of what I was doing," based on "meetings with the RIG and secure conference calls."

He also said he recalled a meeting at the Pentagon in 1986 "in which I went down item by item by item, the things that I was doing, and asked them point blank whether I had to continue to do them to keep the resistance alive."

"These people knew what I was doing," he said. "They knew there was a covert operation to support the Nicaraguan resistance."

Attending the meeting, North said, were Fiers, Abrams, and Assistant Secretary of Defense Richard L. Armitage.

Although North has been depicted as a heroic, never-say-die Marine, as a witness before Congress yesterday he was repeatedly forced to surrender territory that he had staked out.

Initially, he said there had been nothing unusual about the shredding of documents in his NSC office on the afternoon of Nov. 21, after learning of Meese's fact-finding project. But he later acknowledged that there was "increased intensity" in the shredding that day.

He also backed away from an initial assertion that the documents he selected for destruction that day were "personal" papers that he was clearing out because he was preparing to quit and be the "scapegoat." But he eventually acknowledged that he could not deny that the documents destroyed might have been connected with the Meese inquiry.

Initially, North insisted that the Reagan administration's possible violations of law in the 1985 transfers of U.S. arms from Israel to Iran were not a factor in the changing of the official White House chronology of the arms sales last November. But after being referred to notations from his own spiral notebooks he acknowledged that those preparing the chronologies had taken account of the legal requirements in the Arms Export Control Act.

In the summer of 1985, North said that he stopped writing long memos to McFarlane about the contra operations and instead discussed the issue orally or by sending computer messages. After initially denying that the change was the result of congressional requests for such memos, North acknowledged that "I didn't want to show Congress a single word on this whole thing."

North's most emotional outbursts occurred when he was discussing the people and countries willing to support the contras at a time when Congress had prohibited federal aid.

He denounced "the impression that Oliver North picked up his hat and wandered around Washington and foreign capitals begging for money."

"I didn't have to wander around and beg," he declared. "There were other countries in the world and other people in this country who were more willing to help the Nicaraguan resistance survive and cause democracy to prosper in Central America than this body here," referring to Congress.

But Nields led him through a series of questions that showed that Taiwan -- known as Country 3 in the committee's parlance -- provided $1 million only after several solicitations over a nine-month period, including North's personal assurance that the U.S. government approved of such a donation.

In the course of discussing other solicitations, it was disclosed that North 's notebooks recorded a 1985 telephone call from Clair George, the CIA's director of covert operations, who said that South Korea -- Country 5 -- might be willing to contribute $2 million. North said he did not recall the particular call, but added that there had been some conversations "about operation support" and that George had called him because the CIA "knew I was the guy that was in contact with the resistance and was trying to help them out, in compliance with {the law} I would point out."

North also contradicted McFarlane's testimony last May. At that time, McFarlane said that he had lectured his staff regularly that they were not to solicit or encourage contributions to the contras during the time U.S. aid was prohibited.

"I never heard those instructions," North said. Furthermore, he noted that he had given McFarlane a card with the address of an offshore account that would support the Nicaraguan resistance.

"I don't know who he gave it to," North said, "but whoever he gave it to gave a lot of money."

Senior committee members said yesterday that North's testimony was laying the ground work for a deeper examination of the role of the president and his senior advisers in approving or facilitating the 1985 arms transfers from Israel to Iran.

These transactions have emerged as a centerpiece of the final stage of the inquiry, because of efforts last November to conceal the U.S. involvement.

Yesterday's assertion by North that he saw a signed presidential authorization for the November 1985 transaction flew directly in the face of Reagan's statement to the Tower special review board that he did not remember that shipment.

Staff researcher Michelle Hall contributed to this report.