An 18-year-old Fort Hunt High School senior was arrested last night and charged with arson in the blaze that caused an estimated $4.5 million damage to the school early last Saturday, forcing its closing for the rest of the academic year.

Robert Smithwick of 7905 Candlewood Dr., a member of the Fort Hunt High basketball team, was arrested by Fairfax County police at Mount Vernon High School shortly before he was scheduled to paly in a basketball game between the two schools, according to Assistant Commonwealth's Attorney Steven Merril.

The youth was being held in the Fairfax County jail in lieu of $50,000 bond.

Commonwealth's Attorney Robert F. Horan Jr. said he expects police to arrest two more Fort Hunt students and charge them with arson in the school fire within a few days.

If convicted, Smithwick could be sentenced to as much as 10 years in prison, Horan said. A preliminary hearing is scheduled for Monday in Fairfax General District Court.

Smithwick is a second-string forward on the Fort Hunt basketball team. Last night's game with Mount Vernon High originally was scheduled to be played at Fort Hunt, but was moved because of the fire.

Mount Vernon, which is undefeated, won the game, 87 to 48. Fort Hunt's record is two wins and eight losses.

Smithwick was described last night as "quiet, polite and easy to coach" by Jeff Dietze, who is in charge of athletics at the school. Robert Smithwick's twin brother William also plays on the basketball team, as a guard.

The three-alarm fire, discovered about 4:30 a.m. last Saturday, was called the worst school fire in the county's history by a school system spokesman.

Fort Hunt students began attending classes at Groveton High on Thursday.