Seven Northern Virginians were seriously injured late Saturday and early yesterday in four separate accidents in Fairfax County.

Two of the victims remain in serious or critical condition after being struck in hit-and-run accidents.

The first accident occurred about 4:30 p.m. Saturday, when David L. Anderson of 7709 Idylwood Rd. coasted down a hill on Pimmit Drive on his moped and hit a Metro bus driven by Joseph W. Stephens.

Anderson was taken to Fairfax Hospital where he is in good condition. No charges were lodged against Stephens.

Six hours later, at about 10:30 p.m., 17-year-old Jerry Pendley of Vale Road suffered multiple head injuries after a car struck him from behind and threw him 100 feet as he was traveling north on West Ox Road on his bicycle, according to police. Pendley was taken to Fairfax Hospital where he remains in serious condition. Police have made no arrests in the case.

Then shortly after 1 a.m. Sunday morning, four youths were critically injured when the car in which they were traveling swerved across Union Mill Road near Clifton and struck a tree, bursting into flames.

Police said 18-year-old Darryll Leggett was driving a 1973 Ford northbound at a high rate of speed when the car rounded a curve and crossed the road. All four passengers were either ejected or pulled from the car before it fully caught fire, police said.

Leggett and a juvenile, whose name police would not release, were flown to the shock trauma unit at the Washington Hospital Center where they remain in serious condition. Timothy A. Ramey, 18, and another juvenile were taken to Commonwealth Doctors Hospital where they are in critical condition.

The fourth accident occurred about 1:30 a.m., when 32-year-old Margaret E. Good of Arlington darted across Leesburg Pike from Glen Forest Shopping Center near the Arlington County line and slammed into a van driven by 18-year-old David P. Abi-Najm, according to county police. Good was knocked to the ground and then run over by an unidentified dark-colored car that left the scene, police said. She was rushed to Northern Virginia Doctors Hospital where she had surgery and remains in critical condition. Police did not cite Abi-Najm and are looking for the driver of the dark-colored vehicle, which they said may have a vanity license plate.