Some American church leaders say the movie industry is pulling a ruse on the public, making the bad look good by labeling the ugly with a pretty name.

Such is the general assessment by a broad range of churches, Protestant, Eastern Orthodox and Roman Catholic, of the new system under which previously X-rated movies now are rated NC-17.Terming the change by the Motion Picture Association of America a surrender to "sexually exploitative material," officials of the U.S. Catholic Conference and the National Council of Churches said:

"It is an arrogant and ill-advised decision that deeply affects the public good. It was made in isolation, without public consultation. The change is neither in the public interest nor in the best interest of the industry . . .

"Changing the name of the `X' category does not change the nature of the material."

Southern Baptists, the largest denomination not in the council, also endorsed the joint protest. The Rev. Richard D. Land, head of that denomination's social-concerns agency, said:

"The change has all the appearances of watering down an effective wall that helped people stay away from pornographic materials."

Religious publications contended the change camouflages the nature of the formerly "X" category so movie theaters would be more apt to show such films.

It gives moviemakers "a `respectable' category for their excesses," says the Rev. James M. Wall, editor for the Churches' Media Ethics and Advocacy Committee, said the change basically is "about what kind of world our children will live in."

The Catholic Messenger, a diocesan weekly in Davenport, Iowa, says the "marketplace now has more freedom than it had two weeks ago to disturb your children's growth."

The editorial adds that films of "sickening violence and the debased or irresponsible or glamorized fantasy use of sex" will now be "much more widely distributed and shown."

The church critics aren't advocating censorship or government curbs on films, warning that the change itself will provide ammunition for "those who already are calling for regulation of the media."

"That is unfortunate, because a voluntary system of self-regulation that skirts constitutional concerns, yet affords at least a minimum of protection to the public, is workable," the interchurch statement says.

The movie industry contends that the "X" rating has come to be understood as indicating only pornographic films and thus has downgraded some serious, adult films of artistic merit.

Most theater chains don't show X-rated films, and most newspapers won't take advertising for them. Some newspapers, such as the Birmingham (Ala.) News, extended the advertising ban to NC-17 films.

"Smut is still smut," the News editorialized.

In the new system, films considered of some merit but whose sexual or violence portrayals exceed limits for an "R" rating are to be given the new "NC-17" rating, meaning no children under 17 are to be admitted.

The "R" or restricted rating, meaning admission of youngsters only if accompanied by a parent, is continued, with explanations provided on why a film is placed in that category, such as its depiction of sexual activity, violence, profanity, drug use or suicide.

However, no explanations will be given for "NC-17" films.

The motion picture association said they would "continue to be evaluated as X-rated films have been in the past, that is, on the basis that most parents would agree" such films should not be viewed by youngsters.

Wall says "poor enforcement policies" of theaters indicate the NC-17 age restriction won't be effective. Already, he writes, "R" pictures are "easy for 13-year-olds to see, with or without their parents."