DALLAS, NOV. 29 -- President Reagan and his top aides tried to mislead the Tower commission and cover up White House involvement in a key aspect of the Iran-contra affair, former senator John G. Tower says in memoirs scheduled for publication in February.

Tower said he was shocked when Reagan denied that the White House gave advance approval for an August 1985 shipment of missiles to Iran, in contradiction of an earlier statement by the former president.

Portions of Tower's book, "Consequences: A Personal and Political Memoir," were published in today's Dallas Times Herald.

The longtime Republican lawmaker wrote that Reagan's about-face seemed part of a "deliberate effort" to cover up then-White House Chief of Staff Donald T. Regan's involvement in the affair.

Tower was appointed by the Reagan administration in 1986 to investigate the scandal.

The Tower commission report had noted Reagan's shifting stories about the missile sale. But the book marks the first time a principal figure has suggested the changes in the president's story were part of a cover-up.

In a Jan. 26, 1987, meeting with the Tower board, Reagan said that sometime in August 1986, he approved a shipment of arms by Israel to Iran. In a meeting with the commission two weeks later, Reagan said that he and Regan had gone over the matter a number of times and that Regan firmly recalled that the president had not authorized the August shipment in advance.

Reagan said he didn't recall authorizing the shipment, either. Then on Feb. 20, 1987, the president wrote the board a letter, changing his story again. In the letter, he said he simply couldn't recall whether he approved the shipment in advance.