A man was killed and nine people, seven of them children, were injured in a head-on collision in Southern Maryland last night, apparently caused when a motorist swerved to avoid hitting a dog that ran into the road, officials said.

The accident in the 4000 block of Dr. Samuel Mudd Road in Waldorf occurred about 6 p.m. when a 1988 Plymouth Voyager van carrying two adults and five children collided with a 1990 Ford Ranger pickup truck carrying an adult and two children, said Craig Renner, a spokesman for the Charles County Sheriff's office. The van driver, a 46-year-old Waldorf man, died at the scene.

"One of the vehicles crossed the center line, perhaps to avoid a dog that had run out" into the two-lane roadway, Renner said. "The accident is still under investigation."

Both vehicles were heavily damaged in the crash, and both drivers were pinned in the wreckage. The children were taken to the front porch of a nearby home until rescue workers arrived, officials said.

The children suffered relatively minor injuries. Investigators said all of the passengers in both vehicles appeared to have been using safety restraints.

The children were flown by helicopter to Children's Hospital in the District. Girls ages 6, 11 and 12 and boys ages 5 and 9 were reported in fair condition, and a 7-year-old boy and 3-year-old girl were in good condition.

A passenger in the van, described by one official as a trauma nurse who was being taken to work when the accident occurred, declined medical attention. She was taken by ambulance to the hospital where her children were being treated.

The driver of the pickup was taken to another area hospital, but officials did not know his condition last night.

Staff writer Phuong Ly contributed to this report.

CAPTION: The aftermath of a collision between a pickup truck and a van in Waldorf in which one person was killed and nine people were injured.