''Our trucks have traveled 80 million miles since 1975 without recording any personal injuries or major damages to the vehicles,'' said Al Stotts, spokesman for the department's office in Albuquerque, N.M., which oversees the Transportation Safeguards Division. Last month's accident was the most serious of only four recorded in the last two decades, Mr. Stotts said, and it resulted in nothing more than scratches to the trailer.

Such trailers, which can carry up to two dozen bombs, are designed so they can crash and burn without damage to their cargoes. An Energy Department brochure says of them, ''The thermal characteristics of the Safe Secure Trailer would allow the trailer to be totally engulfed in a fire without incurring damage to the cargo.''

The drivers, called ''nuclear materials couriers,'' are trained in counterterrorist tactics. They are armed, and their cabs are bulletproof. Additional guards travel in escort vehicles, generally Ford or Chevrolet vans. The convoys move at night and are tracked by satellite.

The United States stopped producing nuclear warheads in 1990. Since then, a fraction of its arsenal -- about 9,500 bombs -- have been shipped, almost all by truck, to the Energy Department's Pantex Plant outside Amarillo, Tex., for dismantling. Current plans call for trucking an additional 2,500 bombs to the plant for disassembly by the end of the decade.

Further, in its effort to reduce and consolidate the nation's plutonium stocks, the Energy Department has proposed shipping tons of plutonium from military sites around the nation not only to Pantex but also to the Savannah River Site, near Aiken, S.C.

But dismantling was not the apparent purpose of the trip cut short by the storm in Brownlee, Neb., last month. Those bombs are believed to have been on an 800-mile trip from Ellsworth to Pantex for routine maintenance.

''It is quite common and quite routine to have truck convoys on the highways going from military bases to Pantex,'' said Robert S. Norris, a senior analyst on nuclear weapons issues for the Natural Resources Defense Council. ''Right now there are probably convoys going from somewhere to somewhere, as there have been for the last 50 years.''

Alarmed by the increase in road shipments that would result from the Energy Department's plans on plutonium consolidation, one group, the Nuclear Information and Resource Service, has adopted a slogan: ''No Mobile Chernobyls.''