NEW YORK (Reuters) - A protective Plexiglas shield has been placed in front of an elephant dung-stained portrait of the Virgin Mary at the center of a heated battle between the Brooklyn Museum of Art and New York City's mayor, the museum's director said Thursday.

``We are concerned for the safety of that work because of the incredibly high level of rhetoric surrounding it,'' museum director Arnold Lehman said of the piece by British artist Chris Ofili that has offended Roman Catholics, including Mayor Rudolph Giuliani.

Ofili's portrait of a black Madonna, stained with elephant dung and pasted with cutouts from pornographic magazines, is part of the exhibition ``Sensation: Young British Artists from the Saatchi Collection,'' which is scheduled to open Saturday for a three-month run.

As a result of the controversial show, Giuliani has threatened to evict the Brooklyn Museum of Art from its city-owned site and halt millions of dollars in funding. The museum, the second-largest in New York City, receives almost $7 million a year from the city government, about a third of the museum's $23 million budget.

The museum announced Tuesday that it was taking the city to federal court over its threats and hired noted First Amendment lawyer Floyd Abrams to handle the
lawsuit.

Thursday, the city and the museum remained as far apart as ever in the week-long dispute, especially after city officials Wednesday accused the museum of ``hucksterism'' in collaborating with exhibit sponsor Christie's auction house and Charles Saatchi, the owner of the private collection.

A lawyer for the city also said it would take the museum to state court later Thursday or Friday to evict it from the building and withdraw public money. Giuliani maintains that taxpayers' money should not be used for displaying a private collection that he and others find offensive.

Abrams said at Thursday's news conference he ``was retained to take this case and to win it. There are no negotiations going on.''

``Unfortunately, regrettably, sadly, it appears the only place that this matter can end is with a judicial declaration that the mayor acted improperly and unconstitutionally,'' he said.

The exhibit, with its use of pickled cow parts, cut outs from pornographic magazines and human blood, is a showcase for British artists Damien Hirst, Marc Quinn, Chris Ofili and others. It also caused an uproar and drew large crowds when it opened at the Royal Academy of Art in London in 1997.

The Brooklyn Museum and its supporters maintain that while the works are ``challenging and provocative'' banning them would violate free-speech rights.

The Catholic League said it plans to hand out a ``vomit bag'' to each of the first 500 attendees when the exhibit opens to the general public Saturday. The American Civil Liberties Union plans a ``Stop the Censorship'' rally.

The U.S. Senate meanwhile Wednesday agreed to a nonbinding measure calling for the withholding of federal funds from the museum unless it cancels the exhibit.