First Lady Nancy Reagan regularly consulted astrologers to determine the timing of presidential speeches and announcements, former White House chief of staff Donald T. Regan charges in a soon-to-be-published book, informed sources said yesterday.

While Regan attributes to the First Lady most of the responsibility for the astrological consultation and its effect on President Reagan's schedule, an administration official said of the president: "He is definitely aware of it; he approved of it."

The official said the consultation of astrologers by the Reagans to determine the presidential schedule was "a very, very, very closely held secret" because aides "feared the public might misunderstand." The official said that only a handful of aides were aware of it.

A source close to the Reagans said that the First Lady was "motivated by security concerns" and turned to astrological consultation for some of her guidance after the president was wounded in an assassination attempt on March 30, 1981.

A former administration official said that the First Lady would sometimes oppose scheduling an event for a particular date because "the timing was not right," but the official said she never mentioned astrology. Although Nancy Reagan's role in influencing the president's schedule has long been known, her reliance on astrology has not.

Regan's charge that the First Lady frequently relied on astrological consultations was described as "the bombshell of the manuscript" by a source familiar with its contents. Nancy Reagan played a major role in a long and bitter effort to force Regan out of the White House early in 1987 when the administration was demoralized by the Iran-contra affair.

Excerpts from the book, which will be published by Harcourt Brace Jovanovich, are scheduled to appear in Time magazine on May 16. Newsweek made reference to the astrology aspect in its issue published yesterday and NBC News reported it last night.

The president has acknowledged only a passing interest in astrology. In his 1965 autobiography, "Where's the Rest of Me?" Reagan referred to the Los Angeles astrologer, Carroll Righter, as "one of our good friends" and said that "every morning Nancy and I turn to see what he has to say about people of our respective birth signs."

Righter, whose column was syndicated in 166 newspapers, died Saturday at age 88.

A source said the First Lady consulted with more than one astrologer and did not rely principally on Righter after Reagan took office. Another source suggested that more than one astrologer was involved.

After Reagan was elected governor of California in 1966, he decided to be sworn in at the unusual hour of 12:10 a.m. on Jan. 2, 1967, an action that various astrologers as well as the incumbent he defeated -- Democrat Edmund G. (Pat) Brown -- said was determined by astrology.

Reagan denied it through an aide and moved the inauguration up by nine minutes, to 12:01 a.m.

White House spokesman Marlin Fitzwater, asked last night about Regan's charges, said: "I don't know anything about it."

During the 1980 presidential campaign, Reagan responded to the concern of the Federation of American Scientists, which wrote him a letter saying members were "gravely disturbed" that he reportedly made decisions based on astrological advice.

"I have never made a decision based on it {astrology} nor will I ever," Reagan said through his campaign.

When asked to provide examples of how the astrological advice was used, a source familiar with its effect on White House operations cited only scheduling issues, such as the day of presidential travel or the timing of a speech.