A 14-year-old Shaw Junior High School student was in critical condition with a chest wound and three other teen-agers were in police custody last night after one of three motorcyclists allegedly fired a handgun into a group of students near a Northwest elementary school yesterday afternoon, authorities said.

D.C. police said one of the three bikers, who rode two motor scooters past a group of students standing in front of Seaton Elementary School on Rhode Island Avenue NW about 30 minutes after school had closed, shot Tanessa N. Starnes, of 49 U St. NW, as she stood in the crowd.

Capt. William White III, a D.C. police spokesman, said witnesses told police that "one of the three suspects produced a handgun for undetermined reasons and fired" once into the group, striking Starnes, who was taken to Children's Hospital.

When Starnes was wounded, a 3rd District community services officer was at Shaw on other police business, White said, and "one of the witnesses came inside the school and {reported} that there had been a shooting."

Descriptions of the suspects were immediately obtained and broadcast on police radio, White said. Police subsequently arrested a 14-year-old Shaw student and an 18-year-old student at Armstrong Adult Education Center, First and O Streets NW.

The arrests were made in the rear of the 1300 block of Clifton Street NW and at Third and O Streets NW, but it was unclear which suspect was arrested in which location, White said.

Police later released the 18-year-old and arrested two other boys described by investigators as in their "early teens." The two juveniles and the 14-year-old Shaw student were each charged with assault with a deadly weapon.

White said no motive has been established in the incident, but added that the shooting may have been the result of a fight earlier among the suspects and someone believed to have been in the group of students.

"We still haven't confirmed or established if . . . Starnes was a part of the altercation or an innocent bystander who was shot," White said. But "early indications lead us to believe that she may have been an innocent bystander," he added.

White said the scooters were impounded and police are searching for the third suspect and the handgun.