The American Civil Liberties Union is accustomed to being attacked from all sides, including from within. Hordes of its members, for instance, resigned in voluble fury when the ACLU insisted that if the First Amendment did not protect Nazis intent on demonstrating in Skokie, it eventually could not be relied on by decent people either, like members of the ACLU.

It was not, however, until its Biennial Conference in Colorado this June that the American Civil Liberties Union was accused to its face of protecting the "pimps of pornography." Delivering the indictment was Catharine MacKinnon, a UCLA professor of law who had come to the conference to debate the model municipal ordinance she has created to destroy pornography root and branch.

"I wonder if the screams of the victims are inaudible to you," she said to those permissive civil libertarians. "I also wonder if you will continue to side with these pimps."

Prof. MacKinnon has a lengthening list of enemies of her ordinance who are therefore enemies of women. Three more names are now eligible -- the members of a panel of the 7th Circuit Court of Appeals who have unanimously struck down the MacKinnon ordinance as passed overwhelmingly by the Indianapolis City Council and thumpingly approved by Mayor Willam H. Hudnut III. This was the second court defeat for MacKinnon. Earlier, federal district Judge Sarah Evans Barker had, like the 7th Circuit, ruled unequivocally that MacKinnon's ingenious theory happened to leave out the First Amendment.

But that was the point. MacKinnon deliberately designed a weapon against pornography that was a civil rights measure. That way, she figured, she could brush off the free-speech wimps who were bound to hound her. How could a law strengthening civil rights be considered a boon to censors?

Her reasoning was that pornography, since it exploits and degrades women, thereby discriminates against women. Therefore, according to the Indianapolis statute, if a woman walked into a bookstore or a movie or past a newsstand and found herself offended by "the graphic sexually explicit subordination of women, whether in pictures or in words," she would be able to file a complaint with the city's Office of Equal Opportunity. In doing so, she would be a paladin, a woman acting on behalf of all women.

If a court eventually agreed with her, fines would be imposed on the traffickers, and the offending material could be removed forever more.

There are additional punitive dimensions to the MacKinnon ordinance, but this provides some idea of the greatly increased employment the law would give to the Office of Equal Opportunity and the courts. As the feminist Anti- Censorship Task Force said in an amicus brief to the 7th Circuit, "The sweep of the ordinance is breathtaking."

Judge Frank Easterbrook of the 7th Circuit agreed. Would the citizens of Indianapolis, he wondered, be deprived by this law of James Joyce's "Ulysses" and Homer's "Iliad"? Both those works, after all, "depict women as submissive subjects for conquest and domination." We must watch out, the judge said, for solutions to bad speech that leave "the government in control . . . (as) the great censor and director of which thoughts are good for us."

Judge Easterbrook, as well as Judge Barker of the district court, who also gave law professor MacKinnon a failing grade, are both Reagan appointees to the bench. Attorney General Edwin Meese apparently needs to tighten the judge selection procedures somewhat.

Judge Barker made a particularly intriguing point in her dismissal of the ordinance. If the courts were to allow speech that degrades women to be punished, then other groups offended by magazines, books, television and movies could well also get ordinances passed covering them. Blacks, Jews, Catholics, the handicapped, people whose names end in a vowel, would demand equal protection of the law. The First Amendment would drown in deserving exceptions.

Neither judge focused on yet another kind of censorship the ordinance would bring. In its amicus brief, the Feminine Anti-Censorship Task Force pointed out: "The range of feminist imagination and expression in the realm of sexuality has barely begun to find voice . . . as more women's writing and art on sexual themes emerge which is unladylike, unfeminine, aggressive, power-charged, pushy, vulgar, urgent, confident and intense, the traditional foes of women's attempts to step out of their 'proper place' will find an effective tool of repression in the Indianapolis ordinance."

Does Prof. MacKinnon have reservations about women's liberation?