A provider of abortions for more than three decades, Dr. Tiller, 67, had become a focal point for those around the country who opposed it. In addition to protests outside his clinic, his house and his church, Dr. Tiller had once seen his clinic bombed; in 1993, an abortion opponent shot him in both arms. He was also the defendant in a series of legal challenges intended to shut down his operations, including two grand juries that were convened after citizen-led petition drives.

Image Dr. George Tiller, one of the nation's few late-term-abortion providers, was killed in church. Credit... Mike Hutmacher/The Wichita Eagle, via Associated Press

On Sunday morning, moments after services had begun at Reformation Lutheran Church, Dr. Tiller, who was acting as an usher, was shot once with a handgun, the authorities said. The gunman pointed the weapon at two people who tried to stop him, the police said, then drove off in a powder-blue Taurus. Dr. Tiller’s wife, Jeanne, a member of the church choir, was inside the sanctuary at the time of the shooting.

The police in Wichita described the man who was detained as a 51-year-old from Merriam, a Kansas City suburb, but declined to give his name until he was charged. The Associated Press reported that a sheriff’s official from Johnson County, Kan., where the man was taken into custody, identified him as Scott Roeder.

The killing of Dr. Tiller is likely to return the issue of abortion to center stage in the nation’s political debate. Until recently, President Obama, who supports abortion rights, had largely sought to avoid the debate. Last month, he confronted the issue in a commencement speech at the University of Notre Dame, an appearance that drew protests because of his views. During the speech, he appealed to each side to respect one another’s basic decency and to work together to reduce the number of unwanted pregnancies.

Mr. Obama issued a statement after Dr. Tiller’s killing, saying, “However profound our differences as Americans over difficult issues such as abortion, they cannot be resolved by heinous acts of violence.”