William Bennett, former anti-drug policy chief, told President Bush Thursday that he cannot serve as chairman of the Republican National Committee because of "personal and professional obligations," the White House announced.

In a letter to Bush, released by the White House, Bennett told the president he would be unable to serve, mainly because of a previous contract obligation to write two books."I have now determined, with the deepest reluctance, that I cannot serve as both chairman of the Republican National Committee and fulfill these responsibilities," Bennett said in the letter.

Bennett, who resigned recently as the director of the administration's anti-drug office, was selected by Bush for the party post to replace Lee Atwater, who is suffering from a brain tumor. Bennett's name was to be submitted to the RNC for ratification next month.

Before the surprise offer, Bennett said he was resigning from the Office of Drug Policy Control after nine years of public service, including a stint as education secretary, to return to private life.

In informing Bush that he could not accept the RNC job, Bennett cited "a long-standing contractual commitment" to Simon and Schuster to write two books. "They have recently advised, understandably, that they cannot extend my commitment to them for yet another two years," Bennett said.

The outspoken conservative also said he had been advised by his attorneys that federal ethics laws could "limit substantially my involvement in private sector activities" while holding the RNC job for the first year.

"I would not want this to create an appearance of impropriety," he told Bush. Administration officials offered no immediate replacement for the party post, which had been held by the highly effective Atwater until his illness. Under the arrangement with Bennett, Atwater was to retain a role in the party leadership.

Bennett, accompanied by White House Chief of Staff John Sununu, met with reporters outside the West Wing immediately after the announcement.

Bennett said he consulted with three lawyers before making his decision: White House counsel Boyden Gray; Robert Barnett; and his brother, Robert Bennett, counsel for the Senate Ethics Committee. "Each pointed out the need for caution," Bennett said. "It's a gray area . . . questions would be raised."

He said that his brother "was the most emphatic" about taking the RNC job and that he had first been given a "green light from Gray and it turned to yellow and red" on a second reading. "The federal ethics laws are not to be messed with," he said.