Former national security adviser William P. Clark urged President Reagan in a personal letter last August to grant pardons to Rear Adm. John M. Poindexter and Lt. Col. Oliver L. North "before the independent counsel concludes his investigation" of the Iran-contra scandal, according to White House sources familiar with the letter.

Clark, a longtime friend and adviser to Reagan, wrote the letter at the conclusion of congressional hearings on the Iran-contra affair. Clark said that Poindexter, a former national security adviser, and North, the key White House figure in the scandal involving the National Security Council staff, had undertaken their initiatives at "considerable professional risk" and "without consideration for personal gain," according to the sources.

It was learned that Reagan read Clark's letter, which also was sent to White House chief of staff Howard H. Baker Jr. and national security adviser Frank C. Carlucci, and that Reagan personally responded to Clark. It could not be learned what the president's response was.

Clark argued in his letter that a pardon "is not necessarily a recognition that any criminal conduct has occurred," sources said. Clark said further, according to the sources, that a pardon "would simply be an expression of your conclusion that the story has been told, that the people involved have suffered enough, and that neither they, the office of the president, nor the country should be forced to endure an extended criminal trial in which the central issue relates to the creation and implementation of your foreign policy."

White House counsel Arthur B. Culvahouse Jr. responded to Clark in an Aug. 21 letter that said, "We believe that this is not the time for us to engage in a discussion of pardons." A White House official said this language is similar to the response given many Americans who have written letters to Reagan urging pardons for North and Poindexter.

Clark, now in private law practice, said he has never discussed his communications with the president and would not comment on the letter he sent.

The White House has repeatedly responded to news media questions about a pardon by saying it would be premature to discuss one, but officials have never ruled out the possibility. While others -- including former White House communications director Patrick J. Buchanan -- have publicly called for a pardon, Clark's appeal to Reagan is significant because it was delivered privately and because of Clark's standing with the president, the sources said. Reagan appointed Clark to the California Supreme Court and Clark also served as a top State Department official, national security adviser and interior secretary in Reagan's first term.

The disclosure of Clark's letter occurred just as the congressional report on the Iran-contra affair is being made public. Sources said the report will not take a position on a pardon.

The Clark suggestion for a pardon comes as independent counsel Lawrence E. Walsh is presenting evidence to a federal grand jury here with North and Poindexter publicly identified as targets of the investigation. Walsh has indirectly cautioned against using the pardon to short-circuit his investigation.

Some Reagan intimates have argued strongly that the president should not act until he knows what charges, if any, are to be brought against North and Poindexter. Last Dec. 22, before many of the details of the Iran-contra affair were known, Sen. Paul Laxalt (R-Nev.) said in a television interview that Reagan did not intend to pardon the two "because it would not allow the punishment of wrongdoing if there were wrongdoing."

Former White House chief of staff Donald T. Regan testified before the joint investigating committees last July 30 that the subject of a pardon had come up in December 1986, when the Tower special review board was still making inquiries and Walsh had not yet been named. At this point, North and Poindexter were refusing to cooperate with any investigations without a grant of immunity from prosection. At a Dec. 16 White House meeting, aides to the president discussed a possible pardon or urging Congress to grant limited immunity to the two men so they could testify on Capitol Hill.

Reagan that day called publicly for the immunity grant. According to Regan, the president opposed a pardon at that time. "It got shot down right away," Regan testified. "That was something the president wouldn't even listen to, the fact that he should grant a pardon. His reasoning went along this sort of line. To grant a pardon means that you think somebody's committed a crime. You only pardon for a crime, and he didn't know what the crime was."

Regan added, "As yet, there had been no evidence brought to him . . . . So he, the president, said, 'Not only is it premature, but I'll be darned if I'm going to accuse them of a crime in advance.' It never came up again. I mean, he put his foot down hard, and it never came up again."

In an interview Oct. 2 with Fred Barnes of The New Republic, Reagan was asked if North and Poindexter should "spend a single day in jail" for their roles in the affair. "I haven't seen anything that they've done that was breaking the law," Reagan said, adding that it was up to Walsh to determine that. Reagan said "My own personal belief is that they were not involved in anything that was breaking the law."

In his letter, Clark also offered the view that a pardon would be overwhelmingly accepted by the American people, the sources said.

Moreover, Clark said, Reagan would be seen as "a man who, as in the past, stands behind his people in good and in bad times," the sources said. Clark said, "A pardon would also be a clear sign of your resolve to be the driving force of American foreign policy for the remainder of your term in office," the sources reported.

Clark also included "suggested language for an announcement" of the pardons along with the letter, the sources said.

White House spokesman Marlin Fitzwater said yesterday that Reagan received a set of questions from Walsh on Oct. 10 and is planning to respond to them in a sworn statement.