The head of a Boston museum that displayed photographs by Robert Mapplethorpe says politics is the reason why the head of the National Endowment for the Arts rejected a grant for another exhibit there.

"A week ago I would have said no, but now I would say that maybe there is an informal blacklist," said David A. Ross, director of the Institute of Contemporary Art.

NEA Chairman John E. Frohnmayer told Ross he was rejecting a $40,000 grant that would have funded an exhibit by Los Angeles mixed-media artist Mike Kelley.

Ross learned of the rejection only after calling the NEA last week to find out about the grant's status. Since he had not received any notification of rejection, he assumed the April recommendation by the NEA's selection panel for $40,000 had been accepted. The agency told him over the phone that it had in fact been rejected.

NEA spokeswoman Virginia Falck said endowment policy prevented the organization from saying why it rejected the grant, out of consideration for the artist's privacy.

A statement yesterday by the NEA said the council had rejected the application in May, and that Frohnmayer accepted that recommendation but didn't tell the Boston museum because of a clerical error.

"Owing to an administrative oversight, the Institute for Contemporary Art in Boston was not notified," the NEA said.

After talking to Frohnmayer yesterday, Ross said that he finds the agency's explanation unacceptable. "I won't accept this as a standard turndown coupled with a bureaucratic snafu," he said. "... The only reason that this grant was turned down after unanimous peer review approval was that the council and Frohnmayer fear that the work would be politically unacceptable."

Kelley's work includes pen-and-ink drawings, paintings, films and other media, such as stuffed animals arranged in a room to appear as though they are having conversations.

Arthur Cohen, the institute's marketing director, said the only piece of Kelley's art that people might consider offensive was a cartoonish drawing of a man defecating. Kelley's drawings also include depictions of disembodied sexual organs.