Scientists working for the Pentagon have trained ordinary honeybees to ignore flowers and home in on minute traces of explosives, a preliminary step toward creating a buzzing, swarming detection system that could be used to find truck bombs, land mines and other hidden explosives.

The research, under way for three years, initially focused on using bees to help clear minefields. But the effort has broadened, the scientists say. In two tests last summer, before the terrorist attacks on Sept. 11, trained bees picked out a truck tainted with traces of explosives.

The work is in its early stages, and bees, like bomb-sniffing dogs, have limitations. They do not work at night or in storms or cold weather, and it is hard to imagine deploying a swarm to sniff luggage in an airport. But they also have extraordinary attributes, including extreme sensitivity to scant molecular trails and the ability to cover every nook around the colony as they weave about in search of food.

Pentagon officials acknowledge that the idea of bomb-sniffing bees has a public relations problem, a ''giggle factor,'' as one official put it. But that official and scientists working on the project insist the idea shows great potential.