President Reagan answered the charges of duplicity and malfeasance in the Iran-contra scandal by saying last night that he made some mistakes and his policy "went astray," but he did not respond to the many unanswered questions about his actions and those of his subordinates.

Reagan's justification for the Iran arms sales also shifted markedly from earlier speeches. From his first speech on the secret deals in November through his speech on the subject in March, Reagan insisted that his primary motive was to reach out to moderate factions in Iran. Last night he virtually abandoned that rationale; his speech made no specific mention of the strategic opening to Iran.

The president also outlined changes made "so that what we've been through can't happen again, either in this administration or in future ones." But many of the personnel and procedural changes he described last night were implemented last spring after the Tower commission report. Reagan's contention that he has adopted "tighter procedures" on covert actions following the Iran-contra hearings has not quelled the demand of some in Congress for new legislation.

Reagan again returned last night to the defense he has repeatedly focused on since the disclosure Nov. 25 that Iran arms sales profits had been diverted to aid the Nicaraguan contras, saying that he did not know of the diversion or the excess funds. The president said that his former national security adviser, Rear Adm. John M. Poindexter, should have consulted him about the diversion. "No operation is so secret that it must be kept from the commander in chief," he said.

But Reagan did not articulate in last night's speech many other defenses of his actions that White House officials have relayed during the hearings. For example, presidential spokesman Marlin Fitzwater has said Reagan did not agree with Poindexter's testimony that the president would have approved the diversion if he had known about it. Reagan was silent on this last night.

When the hearings focused on the secret network overseen by Lt. Col. Oliver L. North of the National Security Council staff to help the Nicaraguan rebels, White House officials said that Reagan did not believe the NSC staff was covered by the Boland Amendment barring direct U.S. military aid to the contras. Reagan was silent on this last night, too.

Instead, the president focused on broad themes. For example, in describing origins of the Iran arms shipments, Reagan adopted a view similar to the one he expressed after the Tower board report, saying "our original initiative rapidly got all tangled up in the sale of arms, and the sale of arms got tangled up with hostages."

This is sharply different from the portrayal given the congressional committees of what North dubbed "Operation Recovery." Testimony from Reagan's current and former aides described the president as preoccupied from the outset of the Iran deals with winning freedom for the hostages in Lebanon. After a key meeting Dec. 7, 1985, Secretary of State George P. Shultz noted that Reagan had said the American people "will never forgive me" if he let legal problems interfere with the hostage rescue effort. Poindexter recalled the president saying, "I don't feel that we can leave any stone unturned in trying to get the hostages back."

Last night, Reagan acknowledged that "I let my preoccupation with the hostages intrude into areas where it didn't belong. The image -- the reality -- of Americans in chains, deprived of their freedom and families so far from home, burdened my thoughts. This was a mistake."

The president, who watched parts of the televised hearings, said recently that he had not "heard a single word" of testimony indicating that laws were broken. Earlier, he attacked the testimony as being filled with "hearsay." Last night, he was silent on the question of whether there had been illegal actions by him or his staff.

Reagan said last night he "sought to find the answers" once "I realized I hadn't been fully informed" about what his aides were doing. Reagan said "no president should ever be protected from the truth." Last night he blamed others for withholding the truth, although records and testimony produced by the hearings suggest that Reagan also sought to hide parts of the story, from his first claim that there was "no foundation" to the reports of U.S. arms sales to Iran to apparent lapses in memory and contradictory statements before the Tower board last winter.

For example, Reagan told the Tower board that he did not recall the November 1985 shipment of Hawk missile parts through Israel to Iran, which may have violated U.S. law. But three months before he said this to the board, Reagan confessed privately to Shultz that he did know of the shipment, according to Shultz's testimony. Reagan did not reconcile this conflict last night.

Nor did he provide answers on a number of other episodes in the Iran-contra story in which he played a leading role.

For instance, Poindexter testified that Reagan signed on Dec. 5, 1985, a presidential authorization or "finding" for a trade of arms for hostages. White House spokesman Fitzwater has said Reagan does not recall signing the document, which Poindexter later destroyed. Reagan shed no light on this last night.

Reagan said in the speech he was aware of private contributors to the contras and the solicitation of third countries. But he did not address the questions raised in congressional testimony about his role and that of his aides in raising contributions from Saudi Arabia's King Fahd at a time when Congress had cut off all U.S. aid to the rebels.

Reagan gave numerous speeches saying the United States would not pay ransom to terrorists. But former national security adviser Robert C. McFarlane testified that at the same time, Reagan approved a scheme involving agents of the Drug Enforcement Administration to pay bribes to win release of the hostages in Lebanon. Reagan last night did not reconcile his rhetoric with his actions.

The congressional hearings have produced evidence that Reagan was frustrated by congressional limitations and sought ways to get around Congress. Last night, with his once-daunting political standing tarnished by the scandal, he appealed for greater cooperation with Congress, saying "this may be the eventual blessing in disguise to come out of the Iran-contra mess."

But in calling for cooperation with Congress, Reagan failed to note that he has delivered a series of highly confrontational speeches this summer repeatedly attacking Congress on fiscal issues.

At the top of his agenda for the remaining 17 months of his term, Reagan last night put confirmation of Judge Robert H. Bork to the Supreme Court. Reagan claimed that the Supreme Court "has never reversed a single one" of more than 400 opinions in which Bork was in the majority.

That is literally correct, but what Reagan did not mention is that the Supreme Court agreed to review only a fraction of these cases.

Reagan also listed an arms-control agreement with the Soviet Union eliminating intermediate-range missiles as one of his top pri-orities. But he did not even mention his proposed Strategic Defense Initiative, once considered the shining light of his legacy.

Staff researcher Michelle Hall contributed to this report.