A senior Justice Department official and newly released documents yesterday provided evidence of systematic efforts by high-level administration officials last November to cover up and falsify information bearing on the Iran-contra affair.

Assistant Attorney General Charles J. Cooper described how he found himself in a meeting of senior officials who, he later realized, were embellishing a phony story about a November 1985 shipment of arms to Iran, claiming they thought it was a shipment of oil-drilling equipment. Cooper also told how he and two Justice Department associates looking into the affair for Attorney General Edwin Meese III learned that profits from arms sales to Iran had been diverted to the Nicaraguan contras.

But these discoveries, Cooper acknowledged, did not prevent senior administration officials from lying to Congress, falsifying chronologies, misleading the attorney general and destroying key documents.

As the daylong hearing ended, Sen. Warren B. Rudman (R-N.H.), vice chairman of the Senate select Iran-contra panel, said that the committees will soon provide new revelations about the shredding of documents beyond that already disclosed.

Rudman and several other members criticized the informal inquiry conducted by Cooper and his colleagues last November as inadequate and inadvertently incompetent. Meese and his deputies actually "telegraphed" to then-White House aide Oliver L. North the type of evidence they were looking for when North met with them on Sunday, Nov. 23, so that North "knew exactly what to do when he heard what you had," Rudman said yesterday.

Before Cooper was finished, several usually avid defenders of the Reagan administration on the House and Senate panels had leveled uncharacteristic attacks on key figures in the Iran-contra affair. Rep. Michael DeWine (R-Ohio) called North a "liar."

Rep. Bill McCollum (R-Fla.), referring to Cooper's testimony that North, the late CIA Director William J. Casey and former national security advisers John M. Poindexter and Robert C. McFarlane had all misled the attorney general about the November 1985 shipment of Hawk missiles to Iran, said: "If it's not a crime, it's certainly one of the highest acts of insubordination and one of the most treacherous things that's ever occurred to a president, it seems to me, in our history."

From Cooper's testimony and documents presented along with it, the committees learned that:The Central Intelligence Agency drafted testimony for Casey to give to the House Permanent Select Committee on Intelligence Nov. 21 that falsely implied the CIA believed oil-drilling equipment -- not U.S.-made Hawk missiles -- was in the November 1985 shipment. Yet the CIA's own chronology of the Iran initiative, delivered to the White House just a few days earlier, showed that the agency knew the true story.

(Cooper testified that when he first heard the oil-drilling-equipment cover story on Nov. 20, he had no reason to doubt its accuracy. At another point, however, he said he received that CIA chronology showing that the shipment contained Hawk missiles several days before the 20th.) In his actual testimony before the House intelligence committee last Nov. 21, Casey repeated the phony cover story about oil-drilling equipment and added a new misleading twist, that the Israelis had provided weapons to the Iranians "before we got involved." In fact, as the CIA's own chronology shows, the United States was involved in the first, September 1985 transfers of U.S. arms to Iran. And Casey's CIA played a critical role in the November 1985 shipment, leading Casey to personally ask Poindexter to have President Reagan sign a retroactive authorization for that action. North, at a meeting on Nov. 20 attended by Cooper, Meese, Poindexter, Deputy CIA Director Robert M. Gates, and National Security Council attorney Paul Thompson, embellished the cover story by saying no one in the U.S. government knew Hawks had been shipped, and acted as though he was "jawboning" the Iranians to get the missiles back. But as internal NSC memos show, North had been actively involved in the transfer of the Hawks from Israel, and also knew that it was the Iranians who were dissatisfied with the missiles, not the Americans who wanted them back. At a meeting Nov. 21, McFarlane told Meese he first heard about the Hawk shipment when he was being briefed to go to Tehran in May 1986. In fact, McFarlane helped facilitate the Hawk shipment, and was the official who informed Secrtary of State George P. Shultz of that arms-for-hostage deal at the time it was unfolding. Marine Lt. Col. North lied to Meese and Cooper in his interview with the attorney general Nov. 23 that the Israelis told him oil-drilling equipment was involved. At the same time, North told Meese "that he thought it probably wasn't really oil-drilling equipment, but he also . . . made the point that he thought he could pass a lie detector test to the effect that it was oil-drilling equipment," in Cooper's words.

Although Cooper praised the role played by his boss, Meese, in the investigation into the Iran arms sales last fall, his testimony raised questions about the actions of the attorney general and his key deputies. Information contained in Cooper's testimony together with the documents released yesterday suggested that Meese repeated elements of the false cover story at the Nov. 25 news conference during which the attorney general announced that North had been fired and Poindexter had resigned as a result of their roles in diverting to the Nicaraguan contras profits from U.S.-Iran arms sales.

Specifically, Meese declared that Israel had twice shipped U.S. arms to Iran in 1985 without prior U.S. authorization. In fact, Meese already knew from Cooper's research that both 1985 shipments had been authorized by the Reagan administration.

"Both of those transactions took place between Israel and Iran, {and} did not involve the United States," Meese said during the nationally televised news conference.

Rudman was one of several members of the Iran-contra panels who praised the legal qualifications of Cooper and his colleagues, but Rudman criticized Meese for turning to political appointees, and not bringing an experienced Federal Bureau of Investigation agent or criminal prosecutor onto the team making the inquiries. "I think what happened here is . . . we had the world's best cardiologists trying to do neurosurgery. It just doesn't work."

Cooper, a former clerk to Chief Justice William H. Rehnquist, was 34 years old and had no criminal law experience when Meese made him his point man in an internal inquiry into the Iran initiatives last November. Meese has previously been criticized for not bringing the FBI and the Justice Department's criminal division into the inquiry at the outset. He waited to do that until after North was fired -- and, as it turned out, after North had altered and shredded numerous documents.

Meese's sensitivity to the matter was evident from the fact that he assigned Cooper to the probe on Nov. 7, two days after the first American news reports of U.S. arms sales to Iran. But, Cooper said, the attorney general asked him to look into the affair without disclosing Meese's own involvement in critical aspects of it, including the approval of an intelligence "finding" in January 1986 that authorized direct shipments of U.S. arms to Iran in return for the release of American hostages.

On Nov. 17, the CIA provided Cooper with a generally accurate chronology of the U.S.-Iran initiatives, dating to 1985 and including the two U.S.-authorized shipments by Israel of American-made weapons in September and November of that year in association with attempts to release hostages held in Lebanon.

However, when Cooper attended a high-level meeting at the White House three days later to discuss the forthcoming testimony of Casey and Poindexter before the congressional intelligence committees, he did not challenge North's radically different version of the November 1985 events, which included the false cover story that the shipment contained oil-drilling equipment.

When House counsel Pamela Naughton asked Cooper what the reaction of others in the room was, he said they remained silent. (Casey, Poindexter and Meese were among those present.) "They reacted the same way I did," Cooper said. "If that's the way it was, then fine. I mean, they did not appear to me to have any personal knowledge of this matter."

However, one official not present at that meeting chose not to remain silent -- the State Department's legal adviser, Abraham D. Sofaer. He made a series of phone calls to senior officials protesting the misleading testimony being drafted for Casey. Sofaer told them that there were notes of Shultz's conversation with McFarlane about the Hawk shipment in November, according to Cooper's testimony.

Sofaer's own account, given earlier in a deposition to the committees, was released yesterday. Sofaer revealed in that testimony that he had threatened to resign if Casey's testimony was not altered. It was.

Under questioning, Cooper declined to speculate on the motives of those apparently involved in covering up details of the affair. But he said he did not "take it" during an interview with McFarlane Nov. 21 that he was being "entirely straightforward and entirely forthcoming."

After the interview, McFarlane conferred privately with Meese, and Meese later told Cooper what the former national security adviser had told him, "You know, I'm trying and I'm hopeful that I can keep the president's interests uppermost in this. I'm trying to protect the president."

In his own testimony to the committees in the first week of their hearings, McFarlane gave a different account of that talk with Meese. McFarlane said he then told the attorney general privately that Reagan had authorized the first Israeli shipment of arms to Iran in the late summer of 1985.

The other major focus of the testimony yesterday was on the surprise discovery on Saturday, Nov. 22, of the so-called "smoking-gun" memo in North's files that was the first clue that there had been a secret diversion of funds to the contras from the U.S. arms sales to Iran.

That undated, April 1986 draft of a memo from North to Poindexter outlined steps leading up to a high-level meeting of U.S. and Iranian officials in Tehran, and included a suggestion that $12 million of profits generated from the sale might be used to help the Nicaraguan rebels. The document, which was seen by Poindexter and designed for presidential approval or disapproval, is the only paper yet found suggesting a direct presidential link to the controversial -- and perhaps illegal -- diversion. Reagan has denied he ever saw the memo.

Cooper revealed yesterday that Assistant Attorney General William Bradford Reynolds found the document in North's office suite in the Old Executive Office Building that Saturday morning. Because North was in the suite at the time, Reynolds smuggled it out to a luncheon meeting with Meese and Cooper at the Old Ebbitt Grill.

When the men were seated and Reynolds reported what he had found, Cooper testified with a small smile, the attorney general "said something analogous to 'oh, darn.' "

Cooper said that all were aware of the political implications and at one point Cooper called it a "bomb."

Nevertheless, according to Cooper's own testimony, the FBI was not called in, North's office was not sealed, and North himself was allowed to delay a meeting with the attorney general until the next afternoon. North's actions in that interval are expected to be a subject of his questioning next month.

When they met the next day and Meese asked North about a diversion of arms sales profits to the contras, Cooper reported, North was "visibly surprised and not expecting to hear that question." Asked if Reagan had seen the memo, North replied that he "did not think {it} had gone to the president," Cooper testified.

North asked if the document Reynolds found included a cover letter, Reynolds said no.

Meese asked North, "Should we have found one?"

And North responded, according to Cooper, "No, I just wondered."

During the interview, North "offered to reexamine his files and the documents and search for such a cover memo if there was one." Cooper could not recall what the response was to this offer. Meese and his aides presumably did not know that two days earlier -- according to North's secretary Fawn Hall -- North had shredded documents from his NSC safe.

But Rudman took Cooper to task for not asking the FBI to seal North's office until Nov. 28. "You will hear other evidence {about shredding} that will make you feel even worse than you feel now," Rudman said. "By the time you got to looking at things, there was enough shred to fill up half a boxcar and you telegraphed what you were doing to North on Sunday afternoon, and North knew exactly what to do when he heard what you had."

Cooper revealed for the first time yesterday that other forces may have been pushing the administration toward an early public announcement of the diversion at the time Reynolds found the "smoking-gun" memo.

One was a rumor circulating in the CIA that same weekend that a diversion had taken place. Another was a sharp analysis by Sofaer, the State Department legal counsel, who at almost the same time had determined that the sale of U.S. TOW antitank missiles to Iran had generated an excess of funds. In a conversation with Cooper, he also suggested -- accurately, it turned out -- a link between the Iran and contra operations by noting the involvement of Southern Air Transport, a former CIA proprietary, in both.

On Monday, Nov. 24, the Meese team sent one of its members, John Richardson, to search the NSC files for documentary evidence that would challenge the emerging notion that North, Poindexter and McFarlane were the only U.S. officials knowledgeable about the diversion.

Meanwhile, interviews with key officials, including Poindexter and McFarlane, continued. Meese, Cooper said, did not take notes in these interviews because the responses he was going to get "were not going to be difficult to remember."

On Nov. 26, Cooper said, there was a meeting of FBI and criminal division professionals, at which Cooper recalled "an apparent unease" at his presence.

The following day, Thanksgiving, The Los Angeles Times carried a story reporting that crucial NSC documents had been shredded within the last few days.

It was not until the next day, Nov. 28, that the FBI went to the NSC to search for documents.

Late in Cooper's long day of testimony, Rep. Louis Stokes (D-Ohio) asked him: "Based on everything you know about Col. North as a result of your contact with him, your interview of him, let me ask you this: Would you believe him under oath?"

After a pause, Cooper replied, "Congressman, I would not, but I personally don't believe an oath in any way enhances the obligation of truthfulness . . . . I have to regretfully say that."