Hundreds of Contra rebels and supporters are trudging into southern Honduras base camps in a mass exodus, and their leaders say fewer than 2,000 fighters remain in Nicaragua.

Rebel officials blame the U.S. Congress for the retreat, which began four months ago and leaves the smallest Contra force in Nicaragua since the U.S.-backed fighters began their war against the leftist Sandinistas in 1981.More than 1,000 soldiers and civilians returned last week from a central Nicaraguan combat zone. The largest single group to date, about 2,500, was said to be approaching the Coco River frontier.

Contra officials say the combatants, no longer supplied by air drop inside Nicaragua, had to retreat to receive food and other goods now available through the U.S. Agency for International Development, known as AID, in Honduras.

They say the new arrivals joined about 8,000 combatants and 5,000 civilians camped out in tents of plastic and U.S. Army ponchos in the rugged terrain.

By picking up stakes and guiding their supporters along, the Contras have not only lost any fighting edge but their social base, as well.