An early afternoon accident in which a military vehicle damaged a bridge on the H-1 freeway led to hours of near gridlock in urban Honolulu yesterday. State transportation officials and residents alike called it the island's worst traffic jam ever. The trouble began when an Army excavator being towed from Pearl Harbor to Schofield Barracks struck a pedestrian bridge over the H-1 in Aiea, between the Aiea Heights Drive and Kaamilo St. overpasses. The impact shattered the concrete structure and snapped steel support cables within, prompting state officials to deem it unsafe and to close down all westbound lanes of the freeway. Cars packed onto surface streets, the state extending green lights on Kamehameha Highway in an attempt to relieve the pressure. Commuters spent up to six hours in traffic, some circling around the island to avoid the mess, while others abandoned their cars to walk home. Bus riders reported emergency bathroom breaks that involved roadside shrubbery, and hotels welcomed dozens of downtown workers who decided against trying to get home at all. Nimitz Highway was still backed up at 2 a.m. Demolition crews worked overnight to remove the bridge span before this morning's rush hour.