A man walked into a church service in East Selma, Ala., on Sunday morning and opened fire with a handgun, shooting his 24-year-old girlfriend and their infant son and then the pastor before being disarmed by congregants, according to the police.

The police did not identify the victims but said all three were in stable condition after receiving medical treatment. The mother was shot twice, in a shoulder and in her jaw, and the child was wounded in a hand; both were taken to a hospital in Birmingham, Ala. The pastor was treated for a leg wound at a local emergency room, the authorities said.

“The pastor was trying to wrestle the gun from him — the pastor was being a good Samaritan,” said Michael W. Jackson, the district attorney of Dallas County. “But he got shot.”

James Junior Minter, 26, was arrested and charged with three counts of attempted murder, the police said. Mr. Jackson said the shooting appeared to have stemmed from a domestic dispute.

According to the police, Mr. Minter entered the Oasis Tabernacle Church, a small, one-story building, during the morning service and sat next to his girlfriend and his 1-month-old son in the front row. Shortly afterward, he took out a pistol and shot his girlfriend in the face, before turning the gun on the baby, a police statement said.

The pastor, 61, was shot as he grabbed Mr. Minter, trying to subdue him, the police said. Congregants then snatched the gun from Mr. Minter, who fled, the police said.

He was arrested less than a mile away. His vehicle and the gun were recovered at the church, the police said.

“The pastor probably prevented a lot more shooting,” Mr. Jackson said.

“It’s the world we live in now, where people can’t just worship,” he added. “They have to be on alert for other things.”