Former president Ronald Reagan has accused U.S. Senate candidate Oliver L. North of Virginia of lying about Reagan's actions in the Iran-contra affair, saying in a letter released yesterday he is "getting pretty steamed" about "false statements that one candidate continues to make."

In the six-paragraph letter, which comes only days before a significant number of delegates will register for the party's summer nominating convention, Reagan acknowledges that he is violating his own rule against intervening in Republican Party battles.

But as he rises from breezy friendliness to understated anger, the former president accuses North, who served on Reagan's national security staff, of lying about the facts.

"I never instructed him or anyone in my Administration to mislead Congress on Iran-contra matters or anything else," Reagan wrote. "And, I certainly did not know anything about the Iran-Contra diversion. . . . And, the private meetings he said he had with me just didn't happen."

The letter, which was solicited by former U.S. senator Paul Laxalt of Nevada and dated Wednesday, was released by North's GOP opponent, former Reagan administration budget director James C. Miller III.

Miller offered no comment on Reagan's entrance into one of the most watched Senate campaigns in the country. But the letter quickly flushed out North, who derided the effort to involve his former boss as "Washington-insider politics at its very worst."

At a hastily called news conference yesterday afternoon -- surrounded by photographs showing White House scenes of him with Reagan -- North accused opponents of a "blatant and intentional misrepresentation about things I have said and written."

He announced that he had faxed his own letter to Reagan in Los Angeles. His response noted that Reagan was "not taking sides" in the primary but politely corrected the former president.

"You have been seriously and intentionally misinformed about what I have said about my service on your National Security Council staff," North wrote. "It appears that my opponents have intentionally taken out of context and misused my words . . . to salvage a floundering political campaign against me."

However, he continued: "It is a matter of record that I was in many meetings with you in the Oval Office, the White House Situation Room, the Roosevelt and Cabinet rooms and other places in the White House as well."

North's letter also mentioned the 5 1/2 years in which he served the administration "loyally and faithfully" and how "my life and the safety of my wife and four children were threatened by the world's most brutal assassin, Abu Nidal."

"Semper Fidelis," the retired Marine lieutenant colonel concluded.

Despite Miller's silence, prominent North opponents were jubilant yesterday. They have worked for months to draw Reagan into the race, and analysts said Reagan's accusations could be the most serious blow so far to North's high-profile, high-dollar campaign, which as recently as January made him the overwhelming favorite for the nomination.

"When criticisms of Oliver North were made before, by the media or other sources, there was always some explanation North could give," said Mark J. Rozell, a political scientist at Mary Washington College. "He could claim people were out to get him or that they had an ulterior motive."

"But with Ronald Reagan, it's entirely different. He has such stature and conservative credentials that Republicans will listen to him in a way they will listen to no one else," Rozell noted. "If Jim Miller can't turn this into gold, I can't see what else could turn this race around."

The letter's timing could not be better for Miller, who has been behind in the delegate tally by most accounts. Party rules do not require delegates to commit themselves unalterably, and they can easily switch sides until the last minute at the June convention.

The letter certainly marked a 180-degree turn for Reagan, who once referred to North as "a hero." In early 1988, shortly after North and several others were indicted for their actions in the Iran-contra affair, Reagan said: "I just have to believe that they're going to be found innocent, because I don't believe they're guilty of lawbreaking or any crime."

Numerous high-ranking Reagan administration alumni already had turned against North, including former secretary of state George M. Shultz, former attorney general Edwin Meese III and former secretaries of defense Caspar W. Weinberger and Frank Carlucci. North was convicted of shredding documents and lying to Congress about his role in the Iran-contra affair, in which arms were sold to Iran and the profits diverted illegally to Nicaraguan contra rebels. On appeal, his conviction was overturned on a technicality.

North asked Reagan yesterday to let him "set the record straight" and stressed that he had "never said that you told me to mislead Congress." He stated as "a matter of record" the many meetings in which he and the president crossed paths, and the Iran-contra instructions from superiors who reported directly to Reagan.

Only six weeks ago, he discussed the record differently on "Face the Nation."

"The president of the United States . . . said to everybody who knew about it {Iran-contra}, that shall never be revealed," he asserted during the Jan. 30 interview. "The president of the United States sat in a Situation Room meeting and said, 'No one's going to reveal what's going on in this thing.' "

Among those who hailed Reagan's statement yesterday was Virginia Sen. John W. Warner, one of North's most vocal critics in the Republican Party.

"Oliver North has betrayed President Reagan, he has betrayed the American people, and now he is trying to betray the people of Virginia," Warner said. Referring to North's service in the Marines, Warner said, "If his oath of duty, honor and country have any meaning to Oliver North, he will withdraw from the race."

North gave no quarter, though, predicting that Reagan's letter would backfire against Miller and give him a clear nomination victory as early as this weekend.

"Those who have called on me to step aside," he warned, "had better be prepared to wait 12 years until the end of my second term."

". . . But, I do have to admit that I am getting pretty steamed about the statements coming from Oliver North. I never instructed him or anyone in my Administration to mislead Congress on Iran-Contra matters or anything else. And, I certainly did not know anything about the Iran-Contra diversion. In fact, as you know, the minute we found out about it, we told the American people and called for investigations. And, the private meetings he said he had with me just didn't happen."