A judge presiding over one of three federal court challenges to the Partial-Birth Abortion Ban Act (search) questioned Wednesday whether the law is enforceable.

U.S. District Judge Richard Kopf (search) commented during closing arguments in a case brought on behalf of four abortion doctors seeking a nationwide injunction against the law.

The hearing in Lincoln came a day after a San Francisco judge declared the law unconstitutional, saying it places an undue burden on a woman's right to choose. That ruling affects the nation's 900 or so Planned Parenthood (search) clinics and their doctors.

The third case, in New York, is moving toward closing arguments later this month. The law has not been enforced while the cases move forward.

Kopf said he would issue his decision by the end of August.

The federal anti-abortion measure, signed by President Bush (search) last year, bans the procedure known to doctors as intact dilation and extraction, but called "partial-birth abortion" by abortion foes. During the procedure, usually done in the second trimester, the fetus is partially removed from the womb and its skull is punctured or crushed.

Doctors challenging the ban say it is vague and could be interpreted as covering more common, less controversial abortion procedures also done in the second-trimester.

Kopf expressed skepticism to Justice Department lawyer Anthony Coppolino that the government could prove whether a doctor had specific intent to perform the banned procedure.

The judge noted that several doctors testified that they could be unsure exactly what procedure they would perform before they begin.

"How are you ever going to prove that," Kopf asked. "Does the doctor have to give a deposition beforehand so that he can be prosecuted? Why would you enact a law ... that is unenforceable?"

Coppolino said the law addresses only cases where a doctor begins with the intent to perform the banned procedure.

Kopf also criticized as "stupid and superficial" the notion that federal judges impose their personal beliefs in making rulings.

Kopf said he did not think that "one unelected judge, from the hinterlands to boot, ought to veto what Congress does just because he or she doesn't like it. I've never seen a judge like that."

Earlier in the trial, Rep. Steve King of Iowa sat in on testimony and spoke to reporters outside the courthouse.

King, a Republican, said the nation has to re-establish the separation of judicial and legislative powers and that "activist judges" were using their positions to impose their personal views on the rest of society.

Last month, Bush, renewing his support for a proposed constitutional ban on same-sex marriage, said: "The sacred institution of marriage should not be redefined by a few activist judges."

A judge in New York is scheduled to hear closing arguments on June 22 in the third challenge of the ban, brought by the National Abortion Federation, which represents nearly half the nation's abortion providers.

The Partial-Birth Abortion Ban Act is seen by abortion rights activists as the government's first step toward outlawing abortion. Violating the law carries a two-year prison term.