The argument must have seemed second-hand to Catherine A. MacKinnon, the nation's leading crusader for anti-pornography legislation.

But to one young woman in the audience, the potential impact of a pornography ban hit close to home for the first time at a weekend symposium on feminism.

"I am an artist," she told MacKinnon. "I have painted a woman from the waist down. Some men might look at my picture--which is very beautiful to me--and jack off. How is your law going to protect me and my picture?"

Without flinching, the feminist lawyer shot back with a question for the artist. "How do you feel...about living in a society where men use your art in the way you described?"

Reluctantly, the young woman replied, "I can't put things in people's heads, I can't tell them what to feel."

"What if someone who saw something you did went and forced a woman to do it?"

"They're sick and I'm not," the artist responded to a standing ovation.

Not intimidated a second time, the Stanford legal scholar condemned the artist and explained that under a pornography ban she might very well have to sacrifice her work to the cause. "When a pornographer makes something, he doesn't care about other women either."

MACKINNON, THE DRAFTER of Cambridge's November 5 pornography referendum told local feminists that pornography is a longstanding violation of women's civil rights that must be stopped--no matter what the cost to free speech, artistic integrity, or the women's movement itself.

Delivering the keynote address at a local two-day conference last weekend, the feminist lawyer made some hard to dispute arguments about pornography, saying that "it institutionalizes a subhuman, second class, victimized status for women."

"Pornography in the feminist view is not a question of good or bad, false or true, edifying or pleasant, but rather of power and powerlessness," MacKinnon told an estimated crowd of 300 at MIT. "It's a question of sexual politics."

"Because the pornographers have credibility and rights--and women do not--the products of these acts are protected--and women are not. And this is called freedom. Our freedom."

Few would deny MacKinnon's diagnosis that pornography exploits, subordinates and abuses females as well as males. Nor would many disagree with the intent of anti-porn legislation aimed at halting pornographic coercion, force, assault, and trafficking.

What the legal scholar fails to understand, however, is the danger inherent in her ordinance. By defining pornography as simply the "graphic sexually explicit subordination of women through pictures or words," MacKinnon is in effect writing a blank check for unbridled censorship of all printed material.

How are we--or for that matter America's predominantly male judiciary--supposed to know what is "sexually explicit" and what is not? If "sexually explicit" is a legal term, fine. But even Supreme Court Justice Potter Stewart was at a loss for defining prurient material. "I know it when I see it," he said in a famous ruling.