An empty 18-wheel tanker truck jackknifed yesterday afternoon on the rain slick Cabin John Bridge, crashed over a concrete and steel guardrail and fell about 60 feet onto the Maryland bank of the Potomac River.

Rescue workers labored for more than an hour to cut through the roof of the truck and free the driver, Henry D. Smith, 45, of Garland, N.C. He died shortly after the accident in Suburban Hospital in Bethesda from internal injuries.

No one else was seriously injured in the accident, which caused massive traffic jams for nearly three hours on the bridge that carries traffic on the Capital Beltway between Virginia and Maryland.

Maryland State Police said the truck, which normally hauls industrial chemicals, was heading north on the bridge in light rain at about 1 p.m. when it went out of control.

The truck, police said, slipped out of the middle lane of the three-lane northbound section of the bridge and hit a car in the right lane. It then bounced off the bridge's outside guard rail, police said, and into the center of the roadway where it hit a second car.

After that collision, police said, the truck jackknifed and crashed over the left guardrail. The truck fell between the north and southbound sections of the bridge.

Smith, who owned the truck, was driving under a lease for the Central Transport Company of High Point, N.C. He had been driving a truck for 20 years, and was the father of four children.

Maryland State Police attempted to pull the tanker truck up from the river bank yesterday afternoon with a tow truck, but failed. Police said a crane would be needed to move the truck.

The driver of the second car hit by the truck, Johnnie L. Hobbs, 34, of Rockville, suffered pulled muscles in both legs when the truck hit the back of his 1975 Blazer.Hobbs, a typewriter repairman driving home from work, said yesterday he didn't see the truck that hit him.

"I looked through my review mirror a second before it hit and the truck wasn't around," Hobbs said. Hobbs said the accelerator on his car locked and he couldn't stop to see what hit him until he was about one-quarter a mile down the road. Police said there was no apparent structural damage to the bridge.