Two teen-agers were arrested early yesterday and charged with setting a fire at the western Howard County middle school under construction in the 13500 block of Triadelphia Road, West Friendship.

Edward L. Ernst Jr., the deputy state fire marshal, made the arrests after a passer-by saw two people fleeing the school at 12:17 a.m., officials said. The fire destroyed the trash container in which it was set, but the flames were quickly doused by firefighters from West Friendship. Damage was limited to no more than $500, authorities said.

Kellen Tucker, 19, of Ellicott City was being held at the Howard County Detention Center on $25,000 bail on charges of arson and malicious destruction of property, and a 17-year-old was taken to the Alfred D. Noyes Children's Center.