The Pentagon's top procurement regulator disqualified herself from dealing officially with more than 25 defense contractors to whom she wrote exploring business prospects for a consulting firm she may establish after quitting the government, a spokesman said yesterday.

Acting Defense Department spokesman Fred S. Hoffman said "so far there's no reason to challenge the propriety" of the solicitations by Deputy Undersecretary of Defense Mary Ann Gilleece.

Gilleece, who oversees the Pentagon's annual $100 billion procurement of weapons from defense contractors, wrote letters to the prospective clients between May 21 and June 25 to gauge whether her idea of setting up a firm to consult for the defense industry was "viable," she explained later through a spokesman.

She refused to display copies of the letters but said they were written on personal stationery and did not bear her official title.

Hoffman said Gilleece's job, which pays $70,500 a year, will be eliminated in a Pentagon reorganization that includes establishing a post of procurement czar. Defense Secretary Caspar W. Weinberger is expected to fill the post next week.

"She's sending out letters, and she was obviously seeking a way of earning a living after leaving government," Hoffman said.

He said Gilleece sent letters to 25 to 30 contractors after notifying the department's general counsel and formally disqualifying herself "from dealing on behalf of the Defense Department with companies she contacted in seeking future business."

Asked how she can execute her official duties after disqualifying herself from dealing with more than two dozen contractors, Hoffman said, "So far as any specific companies with which she had contact, obviously she cannot perform her duties . There are lots of other companies that do not fall into that group."

Gilleece said later through a spokesman that "virtually none of her responsibilities concern or affect particular contractors. In those cases which do, she recuses herself."