On a balmy Sunday morning, Scott Roeder got up from a pew at Reformation Lutheran Church at the start of services and walked to the foyer, where two ushers were chatting around a table. Wordlessly, he pressed the barrel of a .22-caliber handgun to the forehead of Dr. George Tiller, one of the ushers, and pulled the trigger.

As his premeditated, first-degree murder trial begins Wednesday, no one _ not even Roeder himself _ disputes that he killed one of the nation's few late-term abortion providers.

But what had been expected to be an open-and-shut murder trial was upended Friday when a judge decided to let Roeder argue he should be convicted of voluntary manslaughter because he believed the May 31 slaying would save unborn children. Suddenly, the case has taken on a new significance that has galvanized both sides of the nation's abortion debate.

Prosecutors on Monday challenged the ruling, arguing that such a defense is not appropriately considered with premeditated first-degree murder when there is no evidence of an imminent attack at the time of the killing, and jury selection was delayed. A hearing was scheduled for Tuesday afternoon to give the defense time to respond.

"The State encourages this Court to not be the first to enable a defendant to justify premeditated murder because of an emotionally charged political belief," the prosecution wrote. "Such a ruling has far reaching consequences and would be contrary to Kansas law."

With secret jury selection proceedings stalled, the key questions are now being asked outside the courtroom: Will the judge's decision embolden militant anti-abortion activists and lead to open season on abortion providers? Does the Justice Department plan to file charges against Roeder under draconian federal statutes guaranteeing access to clinics? And what does it all portend for the unfolding case itself and the inevitable legal challenges to the nation's abortion laws?

Roeder, 51, of Kansas City, Mo., has admitted to reporters and in a court filing that he killed Tiller. The prosecution stands ready with more than 250 prospective witnesses to prove it.

News of Sedgwick County Judge Warren Wilbert's decision infuriated Dr. Warren Hern of Boulder, Colo., a longtime friend of Tiller who performs late-term abortions.

"This judge has basically announced a death sentence for all of us who help women," he said. "That is the effect of the ruling. This is an outrage."

Hern said it's irrelevant that Wilbert won't decide until after the defense presents its evidence whether to allow jurors to actually consider a conviction on the lesser charge.

"The damage is done: The judge has agreed to give him a platform," Hern said. "It is an act of incomprehensible stupidity on the part of the judge, but he is carrying out the will of the people of Kansas who are trying to get out of the 19th century."

Kansas law defines voluntary manslaughter as "an unreasonable but honest belief that circumstances existed that justified deadly force." A conviction on that charge could bring a prison sentence closer to five years, instead of a life term for first-degree murder.

A man who runs a Web site supporting violence against abortion providers said in the wake of the judge's decision that he has changed his mind about attending Roeder's trial.

The Rev. Don Spitz of Chesapeake, Va., said he and other activists from the Army of God plan to observe the court proceedings quietly next week.

"I am flabbergasted, but in a good way," Spitz said of the judge's decision.

Spitz acknowledged that the possibility of a voluntary manslaughter defense may influence some people who in the past wouldn't kill abortion providers because of the prospect of a sentence of death or life imprisonment. "It may increase the number of people who may be willing to take that risk," he said.

The Feminist Majority Foundation also denounced the ruling, saying Wilbert essentially was allowing a justifiable homicide defense. The group, which supports abortion rights, urged the Justice Department to file federal charges under the Freedom of Access to Clinic Entrances Act.

Justice Department spokesman Alejandro Miyar declined to comment, citing an ongoing investigation.

In Des Moines, Iowa, even militant anti-abortion activist Dave Leach agreed that the decision opens the door to presenting the same evidence as for justifiable homicide. It was Leach who wrote the 104-page legal brief that Roeder signed and submitted to the court in which he admitted killing Tiller.

"The closer we come to a court actually addressing these issues, the less danger abortionists are going to be in," Leach said. "The violence started in 1992 when FACE was passed, which made the penalty for sitting at the abortion door ... about the same as for shooting an abortionist and ever since the courts have simply not addressed the issues that it looks like this judge is going to take a step to addressing."

As events unfold inside a Wichita courtroom, the Kansas Supreme Court is considering a challenge from four media outlets, including The Associated Press, over the judge's decision to ban reporters from from witnessing jury selection.