A Navy enlisted man fired rifle shots through the windows of a Metro bus and a private automobile on the grounds of the Naval Medical Center in Bethesda last night, then took a hostage and went inside, where he fired two more shots before being subdued, authorities said.

The driver of the Washington-bound bus and a passenger in the automobile both suffered minor injuries, apparently from flying glass, in the shooting, which began shortly after 9 p.m. on the grounds of the medical center on Rockville Pike.

The hostage, a Navy hospital corpsman, was not hurt and no other injuries were reported.

Navy authorities said they could not immediately determine what triggered the bizarre, half-hour-long incident, during which portions of the medical center were quickly evacuated as the suspect approached with what was described as a pump action, clip-loaded .22-caliber weapon.

The suspect, identified as Hospitalman Robert W. Carr, 20, a resident of the barracks on the medical center grounds, was taken into custody last night by Naval authorities. The incident was under investigation late last night by the Naval Investigative Service and no charges had been filed, according to Lt. Cmdr. Ronald D. Arrison, the base public affairs officer.

Arrison said that Carr was in the center's emergency room last night for evaluation of any injury he might have suffered when he was struck over the head with a radio during the struggle to subdue him.

Authorities said that Carr was in front of the towering main building of the medical center about 9:05 or 9:10 p.m. when he began firing at the car and at the bus, which runs from Montgomery College to Dupont Circle NW, making a stop en route on the grounds of the center.

The bus, with seven passengers on board, was approaching a bus stop near the main building when, according to Metro spokesman Cody Pfanstiehl, the driver, Robert King, "saw a guy standing there and thought he was waiting for the bus."

King was about to stop to pick the man up, Pfanstiehl said, when "the man starts shooting."

The driver quickly swerved his vehicle and struck the bus shelter.

Pfanstiehl said two bullets came through the driver's window, but did not strike anyone in the bus. He said the driver "got a little glass in his eye," but was not seriously injured. King was treated at the medical center's emergency room for a laceration of the right cornea, and released.

The base spokesman said that three or four shots also hit an automobile driven by Michael Sheridan.

Although authorities said they were not clear on the sequence of envents, the suspect appeared shortly afterward inside the outpatient building in the new portion of the center, which is south of the main building.

In a short time, he was reported moving through a corridor leading to the inpatient building, and authorities said they ordered a lobby area there evacuated just before he arrived. a professor at an armed forces medical college located at the medi