Three passengers on a Trailways bus were wounded, one seriously, early yesterday when another passenger drew a .38 caliber pistol and began firing as the bus neared the town of South Boston in southern Virginia, state police there said.

They said a man identified as Arthur Ardie Williams, 43, of Fort Washington was charged with malicious wounding in the incident, which occurred about 3 a.m. as the bus was traveling on U.S. Rte. 58 about nine miles west of South Boston.

Police said the gunman, who had been riding in the back of the bus, walked up the aisle firing at random and without warning until he emptied the 5-shot weapon.

The driver immediately stopped the bus, which had 20 passengers, and the gunman fled into nearby woods. Police said the suspect was arrested about 12:30 p.m. after he was spotted swimming in the Dan River about three miles from the shooting scene.

One of the wounded, Ronald Ulmer, 37, of Far Rockaway, N.Y., was shot once in the head and was listed in critical condition at Duke University Hospital in Durham, N.C., police said.

A 19-year-old Long Island City, N.Y., man was shot once in the mouth and was in stable condition at at a local hospital, while the third victim, a 22-year-old North Carolina woman, was treated for a minor chest wound and released.