Many of the nation's leading filmmakers _ including Francis Ford Coppola, Barry Levinson and Paul Mazursky _ will ask the Motion Picture Association of America to change its movie rating system. In a petition to be delivered to the MPAA offices here Tuesday, more than a dozen top directors ask that a new rating be established for adult-oriented films that are not pornographic, according to a copy of the letter. ``The taint of an X rating clearly results in massive and arbitrary corporate censorship,'' the petition says. ``Failure to address this problem will help foster a new era of `McCarthyism' in the arts as during the 50's, when the networks claimed it was not they who blacklisted artists, but the sponsors.'' The letter says the X rating ``has come to be universally recognized as pertaining simply to pornography. ... We therefore strongly suggest that a new rating of A (for adult) or M (for mature) be incorporated into the system to indicate a film contains strong adult themes or images and that minors are not to view them.'' A number of critically acclaimed films _ included ``Tie Me Up! Tie Me Down!,'' ``Portrait of a Serial Killer,'' ``Scandal'' and ``The Cook, the Thief, His Wife & Her Lover'' _ have been rated X in recent months. The petition also was signed by Spike Lee, Rob Reiner, Jonathan Demme, Jim Jarmusch, Ron Howard, John Sayles, Penny Marshall, John Waters, Edward Zwick and John Landis, among others. It follows a similar request made this week by the National Society of Film Critics to the MPAA asking they create a new rating for mature films. Mark Lipsky, the president of film distributor Silverlight Entertainment, said he organized the directors' petition because films with X ratings are denied newspaper and television advertisements and are refused by many theaters. Films carrying the X rating, he said, often are ignored by adult viewers who might enjoy them because the rating has such negative connotations. ``And that's censorship,'' Lipsky said. ``The MPAA is being irresponsible if they don't face the issue.'' A spokeswoman for the MPAA in Washington said the organization would not be able to comment on the letter until next week. Earlier in the day, Jack Valenti, the MPAA president, said the rating system works. A New York judge ruled Thursday that the MPAA's X rating unfairly brands films for mature audiences as pornographic, and called for the organization to devise a new rating system. Judge Charles Ramos, while saying he did not have the authority to change an X rating given to the acclaimed Spanish film ``Tie Me Up! Tie Me Down!,'' called the MPAA ratings system ``an effective form of censorship.'' In a scathing 15-page opinion, Ramos wrote that unless the MPAA reforms the rating system, it might find itself subject to legal challenge. He called on the organization ``to consider the proposals for a revised rating system that provides a professional basis for rating films or to cease the practice altogether.'' He said the problem ``is the need to avoid stigmatizing films of an adult nature, which ought not to be seen by children, but which are clearly not pornographic.'' ``Tie Me Up! Tie Me Down!'' features one sex scene and a brief masturbation scene, and was given an X rating. Many newspapers and movie theaters prohibit advertising and exhibition of X-rated movies.