THE AMERICAN Civil Liberties Union is calling it the case of the "prenatal police patrol."

The San Diego District Attorney's office has filed charges against a woman for her conduct during pregnancy, claiming that her child eventually died six weeks after birth because the mother ignored her doctor's advice and then delayed seeking medical help as she began to hemorrhage.

The police report that after her doctor warned her to stay off her feet and not to take illegal drugs or to engage in sexual intercourse, Pamela Monson took amphetamines and had sex with her husband. Later she began to hemorrhage and lost over a quart of blood, but she did not seek medical help for several hours.

Clearly, Monson grossly neglected her own health. And clearly, her behavior can not have been good for the fetus she was carrying. The issue, however, is what the government can or should do about it.

THE CRIME WITH which Monson has been charged is to "willfully omit, without lawful excuse" necessary medical care for her child. Under the provisions of this 1926 law, fetuses are considered persons. The statute has been used primarily to force husbands to furnish child support for families they have deserted; the fetus has been considered a child in order to make the father responsible for it.

However, while ascribing rights to a fetus may be a convenient way to argue for child support, Monson's case shows it to be a slippery slope toward granting the state an interest not only in the conduct of its citizens, but also in their bodies.

Monson acted immorally by almost any ethical standard, but mere immorality is not an argument for state sanctions or control. The question is whether the state has a legitimate interest in the way a woman treats her own body during pregnancy.

If the answer is yes, then how is that interest to be defined? As far the health of a child is concerned, its mother's conduct at any time during pregancy could be crucial. In fact, Substances a woman might consume even prior to conception could conceivably have profound and deleterious effects on a child. Are we to consider women's bodies the nation's breeding ground and therefore to regulate what women may eat, drink and breathe and how much they should exercise?

Obviously, no one would take the argument this far. But then how do we demarcate when a woman is to be considered legally responsible for her conduct during pregnancy? We are faced with the same insoluble question that makes abortion such an intractable issue: when does a fetus become a human being that has legal rights and stop being part of its mother's body?

And suppose we were to settle, arbitrarily or otherwise, upon a time when a fetus could be considered a legal person--let's say the third trimester, currently the time at which abortions can be prohibited. What then is proper conduct for a mother during her third trimester?

Should it be a crime for her to smoke cigarettes? Should she leave the room if others do? What about drinking beer or diet soda or catching a cold because she callously decided to go outdoors without a hat?

THE ANSWER should be obvious. Allowing the state an interest in a woman's conduct during pregnancy means giving it an interest in how she treats her own body, and that is an unacceptable intrusion into her privacy, an egregious violation of her person.

Pamela Monson did a horrible thing. She has to live with the choices she made, but those choices are not something for the state to decide. If government has an interest in the health of its citizens and of the next generation, let it give them the education and the opportunities they need to lead happy, healthy lives. Until it does, policing their bodies is no substitute.