Recently I have read of ''fetal protection'' policies at Johnson Controls {news story, Oct. 11}, parents prosecuted for failing to seat-belt their children, and now there is Nat Hentoff's astonishing article on prenatal care {op-ed, Jan. 19}. Shouldn't we be a little more concerned about the state's willingness to violate the rights of some citizens for the sake of their children -- or ''children-to-be,'' as Mr. Hentoff puts it, even though the Constitution gives fetuses no legal existence?

If the state's compelling interest in child welfare permits it to jail parents who risk harming their children, who will decide what level of risk is acceptable? We may easily justify jailing those who abuse illegal drugs, but what of legal substances or practices? Can pregnant (or, as in the case of Johnson Controls, ''potentially pregnant'') women be barred from consuming alcohol, tobacco or sugar-free sweeteners? If California can limit women's hours in front of a computer terminal, will other states curtail TV-watching time or prohibit women from standing less than 20 feet from an operating microwave? Are those who would restrict women's earning potential and freedom willing to underwrite adequate medical treatment, or will finding care be another of those ''maternal responsibilities'' invoked by Mr. Hentoff?

The state may justly intervene in most cases of demonstrated child abuse, because there the parent-child bond is already severed. To punish parents for not eliminating all risks to their children -- and who among us can do this? -- is to alienate a child's surest ally for the sake of dubious health benefits. Those who wish to see healthy children should target conditions inhospitable to motherhood, not mothers. KARIN CIANO Williamsburg