Air Force technicians on Friday began dismantling the Minuteman III rocket that was being transported from Montana to Utah when the tractor-trailer hauling it flipped on its side as it entered a weigh station off a desolate desert stretch of I-15 in eastern Idaho.

The interstate and intersecting Idaho 33, which were closed down for seven hours on Thursday after the accident occurred, were shut down for another three hours Friday morning to facilitate work on the wreckage.State police said the highways would be closed for about three hours again Saturday morning as technicians perform the final work needed before the pieces of the three-stage solid fuel rocket can be trucked to Hill Air Force Base.

An Air Force Safety Board was investigating the accident, which occurred about 25 miles northwest of Idaho Falls. But initial indications were that an unexpected shift of the rocket in its enclosed trailer caused the rig to flip on its side on an off ramp to the state Transportation Department's Sage Port-of-Entry.

The rocket, about 45 feet long, 6 feet in diameter and weighing 50,000 pounds, was being shipped from Malmstrom Air Force Base near Great Falls, Mont., to Hill for routine maintenance when the accident occurred shortly before noon Thursday.

The rocket did not include the missile warhead, guidance system or liquid propulsion rocket engine. And while it was loaded with solid fuel, Air Force technicians said that substance is stable and "chances of an explosion are extremely remote."

The transport's civilian driver, Barry Hatch, 35, an employee of Uintah Freightways in Salt Lake City, was in good condition at an Idaho Falls hospital with a broken wrist, dislocated elbow and minor injuries.