As Donald Regan defends the right of former White House aides to relay private stories, President Reagan is defending the first lady with a warning relayed to the public: "I'll be damned if I'll just stand by and let them railroad my wife."

Regan, embittered at how he was dumped as the president's chief of staff in a backroom coup engineered by Nancy Reagan, has returned to the spotlight with a vengeance, seeking vindication and perhaps a last laugh.After a week of promotional hype aided by his exposure of a White House where presidential schedules were guided by astrological forecasts, Regan's new book hit the stands Monday with the force of a powerful political right hook.

The White House is reeling from his depictions of the president as a detached chief executive who "laid down no rules and articulated no missions for his administration" and of the first lady as an obsessive and meddlesome wife who intruded into every facet of business from personnel to policy.

The Reagans are livid. The public appears temporarily intrigued and even amused by the tales of stargazing and back-stabbing at the highest levels of government. And for his part, Regan seems to savor the furor.

"I have no great bitterness in me, and I'm much more relaxed now," he told United Press International Monday. "I have a right to tell my side of the story. Everybody else has."

Indeed, a slew of former aides and advisers have emerged recently with books about their White House days, and Reagan has grown increasingly frustrated. But at lunch in the Oval Office Monday, the president made clear to columnist Carl Rowan just how angry the latest tome has made him - and why.

"He told me, `I'll be damned if I'll just stand by and let them railroad my wife,' " Rowan recalled later to local television station WUSA.

Asked what recourse may be available, however, a more resigned Reagan told the journalist, "I guess I'll just have to sit and let things cool down and make a decision on how to deal with this thing."

Rowan reported the president branded Regan's book "a bunch of falsehoods" and said the first lady "feared she had brought

all this down on (my) head." Rowan quoted the president as reassuring his wife, "No, honey, I brought all this on your head by taking this job."

For her part, Mrs. Reagan said through press secretary Elaine Crispen, "I was taken aback by the vengefulness of the attack. It's come through to me that Don Regan doesn't really like me."

White House spokesman Marlin Fitzwater described Mrs. Reagan as "very upset" by the "kiss-and-tell story in the mold of all such books which seek to exploit the presidency or the first family for personal self-interest."

But Fitzwater had to pick his way through a political minefield in defending the first lady's interest in her husband's affairs as well as her right to turn to astrology or other sources for personal comfort and guidance.

"There's nothing wrong with the first lady or anyone else consulting an astrologist," he said at one point - before stonewalling uncomfortably when bombarded with questions about whether Mrs. Reagan would keep using astrology to influence scheduling decisions and whether the president approved of it.

"I don't think it's a relevant issue," the spokesman said.

There is little the White House can do but to hope the initial shock waves from the Regan book will subside and to minimize the revelations. The best damage control efforts cannot erase the damage that has been done.

On Capitol Hill, Sen. John Rockefeller, D-W.Va., said Regan and former White House spokesman Larry Speakes, who painted a similarly unflattering portrait in a book published last month, had "humiliated" Reagan "for their own gain."

Calling their actions "despicable," Rockefeller said the two men had "set the standards for indecency in public service."

Regan, promoting his $21.95 book, dismissed financial gain as a motive. The ex-Marine who amassed a fortune of $40 million or more in a Wall Street career that took him to the chairmanship of Merrill Lynch & Co. said book proceeds - including a $1 million advance and $125,000 from the publication of excerpts in Time magazine - would go to charity.

Regan maintained he merely sought to draw "a candid portrait" of Mrs. Reagan.

"If it's embarrassing to them it's only because it's a true history," Regan told NBC News. "This is not a state secret; it has nothing to do with national defense. This happens to be a little family secret that I have brought out."