Someone opened fire on a station wagon in an Annapolis town house development early yesterday morning, critically wounding two women with a single bullet as they sat in the vehicle, police said.

Shortly afterward, David Allen Sumrall, 21, a capenter described as distraught since his separation from his wife last month, surrendered peacefully to police and was charged with two counts of assault with intent to murder.

The 1:30 a.m. incident brought screams of panic at Heritage Court, a town house community located about a mile southwest of the city's historic downtown district. Police yesterday gave no motive for the bizarre shooting, and a friend said Sumrall apparently knew neither of the shooting victims personally.

According to police reports and other accounts, a large-caliber bullet smashed through the rear window of the station wagon in a parking area near Sumrall's house and struck Nancy Walton, 25, a resident of the development, in the back, and Wanda Melton, 28, a visitor from Pensacola, Fla., in the shoulder.

Walton was listed in critical condition yesterday at Anne Arundel General Hospital after emergency surgery. A state police helicopter flew Melton to the University of Maryland shock trauma unit in Baltimore, where she was said to be in critical but stable condition.

Police answering calls of alarm secured the area and ordered everyone in a house identified by neighbors as the source of the gunfire to come out. A lone man identified as Sumrall walked out unarmed with his hands over his head and was arrested.

Annapolis police, acting on a tip that the house might contain booby traps, explosives and another suspect, called in a Maryland state police team that specializes in hostage seizures and tactical asault. The team tried unsuccessfully for several hours to contact anyone still in the house, then entered it and found no one there and no traps or explosives.

Sumrall was being held yesterday without bail at Anne Arundel County Detention Center.

William Keller, 23, a cement companyemploye who rented the $350-per-month town house with Sumrall, said Sumrall had been upset over his recent separation from his wife, who had lived with him in the house until last month. The couple are engaged in a custody battle over their only child, born in December, Keller said.

Keller, who said he had left the house for the evening about six hours before the shooting incident occurred, said Sumrall did not appear unusually upset.

Sumrall was described by Keller as a man with a deep interest in firearms.He kept two long guns on a wall rack inthe house, one a functional muzzle-loading weapon from the Civil War era. He also owned a Civil War uniform and last fall participated in a reenactment of a historic battle, Keller said.

Police refused to provide information about the weapon used in the incident.

Keller yesterday described Sumrall as congenial and a good roommate. "Friends keep calling up saying they heard it on the radio and couldn't believe he'd do a thing like that," Keller said.