The skies were rainy and dark and the winding two-lane road was slick when a car carrying four Sherwood High School students crossed the center line of New Hampshire Avenue about 2:30 p.m. yesterday and collided with a bus carrying their schoolmates, Montgomery County police said.

One teenager, riding in the back seat of the convertible Chevrolet Cavalier, suffered massive head injuries when he was partially ejected from the rear passenger window, police said. He was taken in a state police helicopter to the Maryland Shock Trauma Center in Baltimore, where he was listed in serious condition.

Police said they do not think he was wearing a seat belt. "You don't get thrown halfway out of a car unless you're not wearing seat belts," said Lt. George Bransom, of the Montgomery police.

The driver of the car and another passenger were taken by helicopter to Suburban Hospital, where they were reported in stable condition last night. A fourth student was treated at Montgomery General Hospital. Information on the fourth student's condition was unavailable.

No one on the bus was seriously injured, police said, but a 16-year-old girl was taken in an ambulance to Montgomery General for observation.

No names were released, though police and school officials said all the students involved were from Sherwood High School.

Police were investigating the crash. Initial police reports suggested that the driver of the Cavalier lost control while traveling south on a narrow, wooded and windy section of New Hampshire Avenue near Brighton Knolls Drive. The car crossed the center line and collided with the driver's side of the school bus, police said. The car then lost a back wheel and went into a spin, investigators said.

Investigators said the heavy rain that began falling yesterday afternoon may have been a factor. "You have oil rising to the surface, and this could have caused the accident," Bransom said.

At the scene, the two-door car blocked one lane, the front hood and bumpers ripped off, the windshield smashed and the engine mangled. Pieces of glass and other debris were strewn across the road.

School officials said a team of school psychologists and other trained counselors would be sent to Sherwood High today.

Staff writer Steven Gray contributed to this report.

CAPTION: Montgomery County investigators inspect the accident scene. All of the injured students were from Sherwood High School, authorities said.

CAPTION: A damaged school bus and a smashed-up car block opposite lanes of New Hampshire Avenue in Montgomery County after a collision yesterday.