A federal judge on Friday offered to let a medical expert help him decide a case challenging the Partial-Birth Abortion Ban Act (search) to dispel possible perceptions of bias toward the plaintiffs.

U.S. District Judge Richard Kopf (search) made the announcement from the bench as the Justice Department was preparing to call its last witness in the case.

Kopf said he would be willing to work with both sides to appoint an outside expert after all testimony in the trial is heard. He said he would discuss his proposition with lawyers from both sides after testimony ends Friday.

In making the offer, Kopf noted comments earlier this week by Rep. Steve King (search) that activist judges were using their positions to impose their personal views on the rest of society.

King, an Iowa Republican who sat in on testimony Monday, said outside the courthouse that the nation must re-establish the separation of judicial and legislative powers.

"Congress determined that a partial-birth abortion is never necessary to protect the health of the mother," said King, a member of the House Judiciary Committee. "I don't think it's possible for a single judge to sit in a courtroom and substitute his findings for the findings of 435 congressmen."

On Friday, King said Kopf's offer to work with a medical expert did not alleviate his concerns. Congress heard from many experts and constituents over eight or nine years before it passed the law, King said.

"It's virtually impossible for a court to gather that kind of information to overturn the decision made by the people of America through their voice in the entire U.S. Congress," King said.

The abortion ban was signed last year by President Bush but has not been enforced because judges in Lincoln, New York and San Francisco agreed to hear evidence in three simultaneous non-jury trials on whether it violates the Constitution.

Kopf said he wanted to be as fair as possible in handling the case and "to dispel any notion that this court ... has some agenda other than finding the facts truthfully."

King, who said he opposes abortion except to save the life of the mother, said Congress should consider legislation that would prohibit judges from ruling on legislation dealing with certain subjects, including abortion and same-sex marriages.

Lawyers from the Center for Reproductive Rights (search) challenged the law on behalf of Nebraska abortion provider Dr. LeRoy Carhart (search) and three other physicians.

It was Carhart who brought a challenge that eventually led the U.S. Supreme Court in 2000 to overturn Nebraska's ban on a procedure doctors call "intact dilation and extraction," or D&X. Opponents call it partial-birth abortion. The high court said the Nebraska law and others like it were an "undue burden" on women's rights.

Kopf also presided over Carhart's challenge to the Nebraska ban.

In blocking enforcement of the federal ban on D&X procedures last year, Kopf cited concerns that the law did not contain an exception for preserving the health of a woman.

During the procedure, generally performed in the second trimester, a fetus is partially removed from the womb and its skull is punctured or crushed.

The Bush administration has argued that the procedure is "inhumane and gruesome" and causes pain to the fetus.

On Thursday, a doctor testifying in favor of the ban acknowledged that crushing the skull of a fetus may be necessary in other, more common types of abortion.

The acknowledgment by Dr. Elizabeth Shadigian, an obstetrician and gynecologist at the University Of Michigan, was a major victory for Carhart's side.

Carhart testified earlier that the ban is so broad that it could be interpreted as covering more common procedures, including "dilation and evacuation," or D&E, which sometimes result in a fetus being removed whole.

Shadigian testified earlier that there is no evidence that a D&X is ever necessary to preserve the health of the mother.

Doctors who use the D&X procedure have said it is sometimes the safest abortion method. Shadigian said that has not been proven.

"It's just anecdotal evidence that they think it's safe," she said. "Medicine is based on evidence."

About 1.3 million abortions are performed in the United States each year, and almost 90 percent occur in the first trimester. The total includes an estimated 140,000 D&Es and 2,200 to 5,000 D&Xs.