Any parent who has rejoiced at seeing a sonogram showing the image of a second-trimester fetus knows how much it looks like a baby. And any parent who has seen a baby blossom into a vibrant teenage girl can imagine the agony of hearing her plead for help in aborting a pregnancy that she had hidden for three months. But any parent who would know with certainty what to say to that teenage girl must be smarter than I am.

Under "partial-birth" abortion laws adopted by many states, twice passed by Congress, and twice vetoed by President Clinton, one option would apparently be illegal: the most common (by far), and probably the safest, form of second-trimester abortion. That’s the basis of three decisions issued on Sept. 24 by the U.S. Court of Appeals for the 8th Circuit, striking down "partial-birth" abortion laws in Nebraska, Iowa, and Arkansas.

The unanimous 8th Circuit rulings — written by a Carter appointee and joined by two Reagan appointees — are the latest in a line of opinions joined by some 26 judges, including 11 Reagan and Bush appointees, suggesting that "partial-birth" abortion laws are unconstitutional. Four judges thus far have suggested the contrary.

Right-to-life advocates have sold much of the public, and many legislators, on the myth that "partial-birth" abortion laws would outlaw only an especially grisly (and rare) way of killing third-trimester fetuses on the verge of birth.

False. Some 28 of the 30 state "partial-birth" abortion laws would ban certain procedures to abort fetuses at any stage of pregnancy — including fetuses that are not yet viable, and arguably including some in the first trimester. The laws except only abortions necessary to protect the life of the woman. And many of them threaten doctors with criminal penalties as harsh as life imprisonment for using abortion procedures that are morally indistinguishable from other procedures that would not be restricted.

Below I describe two abortion procedures used in the second and third trimesters. Both — indeed, all abortion procedures — are gruesome to contemplate. This may help account for the reluctance of some of us (including me, until now) to ponder in detail whether particular procedures should be banned.

Advocates of "partial-birth" abortion laws claim that they would restrict only an extremely rare procedure called dilation and extraction (D&X). It involves pulling the fetus, feet first, from the uterus, through the cervix, and into the vagina, except for the head; using scissors or another surgical instrument to rupture the skull; and then suctioning out the brain. The more the abortion debate has centered on this image of the dismemberment of nearly born babies — rather than on the plight of women with unwanted pregnancies — the better the right- to-life side has done in the court of public opinion.

Thus was Senator Daniel Patrick Moynihan, D-N.Y., for example, persuaded that "partial-birth" abortion is so "close to infanticide" that it should be outlawed. But if Moynihan thought he was voting to restrict only late-term abortions, he was misinformed. As the 8th Circuit held, "partial-birth" abortion has "no fixed legal or medical content." It means whatever a legislature defines it to mean. And under most definitions, these laws are very broad.

The laws in many states, and the measure that passed Congress in 1997, outlaw abortions in which the doctor kills the fetus after pulling any "substantial portion" from the uterus into the vagina.

And that, the 8th Circuit said, is precisely what doctors do, not only in D&X abortions but also in "dilation and evacuation" (D&E) abortions — the most common method in the second trimester. D&E abortions typically involve using forceps to pull an arm or a leg from the uterus into the vagina and then dismembering the fetus.

In striking down the three statutes, the 8th Circuit cited Supreme Court precedents, including the 1992 ruling in Planned Parenthood vs. Casey that a state may not place "a substantial obstacle in the path of a woman seeking an abortion" of any fetus that is not yet viable.

In an effort to dodge these precedents, those who defend "partial-birth" abortion laws in court have interpreted them as narrowly as possible, resorting to some bizarre distinctions. Thus, in disputing the view that "partial-birth" abortion laws (or some of them) would restrict D&E abortions, the laws’ defenders argue that they would restrict only procedures in which fetuses are intentionally dismembered and killed after being pulled into the vagina (D&X) — and not procedures in which fetuses are dismembered and killed while being pulled into the vagina (D&E).

Think about that distinction.

A three-judge panel of the 8th Circuit showed that the Nebraska, Iowa, and Arkansas statutes in fact make no such distinction. Written by Judge Richard S. Arnold — a Carter appointee (and Little Rock friend of President Clinton’s) — the three 8th Circuit opinions were joined by Chief Judge Roger L. Wollman of the 8th Circuit and Chief Judge Paul A. Magnuson of the U.S. District Court in Minnesota. Both are Reagan appointees.

The 8th Circuit left it to others to ponder why, as a matter of morality or common sense, the legality of an abortion should turn on where in the birth canal various parts of the fetus are located when it is killed.

Chief Judge Richard A. Posner of the U.S. Court of Appeals for the 7th Circuit tackled that question last November in a decision (now being reviewed by the full 7th Circuit) that preliminarily enjoined Wisconsin’s "partial-birth" abortion statute.

"The constitutional right to an abortion carries with it the right to perform medical procedures that many people find distasteful or worse," wrote Posner, a Reagan appointee. "The singling out of the D&X procedure for anathematization seems arbitrary to the point of irrationality. Annexing the penalty of life imprisonment to a medical procedure that may be the safest alternative for women who have chosen abortion because of the risk that childbirth would pose to their health adds a note of the macabre to the Wisconsin statute."

I’m with Posner. I can well understand why some critics of Roe want to outlaw any procedure that destroys a fetus, especially in the later stages of pregnancy. I can’t understand why the legality of an abortion should not turn on the safety of the procedure, or the health of the woman, or the stage of fetal development — but rather on exactly how far into the birth canal the fetus is pulled before being destroyed.

"No argument is made," as Posner wrote, "that if a fetus feels pain, the pain feels worse when the fetus is killed in the birth canal than when death occurs a moment earlier in the womb."

Posner also punctured the implausible claims that "partial-birth" abortion laws don’t burden women seeking abortions, because an equally safe, legal alternative procedure is always available. If this were so, Posner wrote, the statute "cannot discourage abortions — cannot save any fetuses — but can merely shift their locus from the birth canal to the uterus."

Conversely, such a law "can save fetuses only by endangering pregnant women, since the only time a woman denied a partial birth abortion will decide to carry the fetus to term is when the alternative methods of abortion would pose a greater risk to her."

And if (as some evidence suggests) "partial-birth" abortion laws, in fact, would block some women from access to the safest abortion procedure, the laws also conflict with Roe’s holding that even post-viability abortions may not be restricted in ways that would endanger the woman’s life or health (including emotional health).

None of this is in the Constitution, of course. That’s why Roe is so hard to defend as an exercise in constitutional interpretation. But even if the Supreme Court was wrong to constitutionalize abortion in 1973, the question on the table is whether "partial-birth" abortion laws make any sense now.

To return to where I started: If I had a daughter who (after due consideration of all options) wanted a second- trimester abortion, I’d probably swallow my misgivings and help her get one. If the safest abortion procedure were illegal where we lived, I’d take her to another state, or another country. If the fetus were viable, I might feel differently. But even then, my main concern would be my daughter’s health, including her mental health.

That’s why I would not support a "partial-birth" abortion law, even if it was limited to viable fetuses — and why I see no sense in these laws as written, most of which would deny the safest abortion procedure to women at earlier stages of pregnancy.