The Bush administration urged a federal appeals court Thursday to overturn a judge's decision nullifying a congressional ban on a type of late-term abortion.

The case before the 9th U.S. Circuit Court of Appeals is one of three in which federal judges have ruled that the ban is unconstitutional. Last month, the Bush administration asked the U.S. Supreme Court to hear another of the cases.

The 2003 Partial Birth Abortion Ban Act -- which never went into force -- bans a procedure carried out in the second trimester in which the living fetus is partly removed from the womb, and its skull is punctured or crushed. The law allows a doctor to cut up a fetus before it is removed from the woman.

Abortion rights advocates say the law is vague and could halt almost all second-trimester abortions.

The government argued that Congress determined the procedure is never medically necessary, and therefore a woman's options for an abortion are not limited.

Judge Sidney R. Thomas wondered whether Congress's findings "matter at all," given the conflicting testimony of doctors in lower courts. Judge William A. Fletcher said a doctor may end up performing the banned method during an abortion "in order to do it properly" and "for the health of the woman."

Assistant U.S. Attorney Gregory Katsas said that "there are medical arguments on both sides," but the court should defer to Congress's findings.

The court did not indicate when it would rule.