A truck driver was critically injured yesterday, and traffic of the Capital Beltway was backed up for miles just before the rush to get away for the Labor Day weekend when a tractor-trailer truck collided head-on with another truck in North Bethesda and burst into flames.

Two other persons were less seriously hurt in the crash that led to at least two smaller collisions.

According to Montgomery County police, the driver of the truck, Elliott Tyler Jr., 49, of Keswick, Va., failed to negotiate a curve as he was traveling west on the beltway between Connecticut Avenue and Rockville Pike.

Tyler's truck plowed through an opening in the barrier separating eastbound from westbound traffic and struck a flatbed truck. A pickup truck and a passenger car piled up behind the two trucks, police said.

Tyler was in critical condition at Washington Hospital Center with multiple fractures and internal injuries. His left foot was amputated in the accident, a spokesman for the hospital said.

The driver of the second truck, Samuel Pinkney, 38, and his passenger, Randolph Teagoe, 30, both of Baltimore, were reported in satisfactory condition in Suburban Hospital in Bethesda.

Police said the accident occurred about 1:15 p.m. Traffic on the beltway was closed in both directions for a half-hour and eastbound lanes were closed until 3:30 p.m.

Police said eastbound traffic was backed up about three miles, stretching into Virginia.