CHATTANOOGA, Tenn. — Bob King has pursued one goal above all as president of the United Automobile Workers — to unionize several foreign-owned auto plants in the South. He said he viewed that as pivotal if his once-mighty union was to gain numbers and strength after decades of decline.

The first step was to unionize the Volkswagen plant here, but Mr. King was stunned by the results of the unionization vote announced late Friday. In one of the most closely watched unionization elections in decades, the U.A.W. lost, with workers voting, 712 to 626, against joining the union.

This will slow and perhaps derail Mr. King’s ambitious plans to unionize other plants in the South. For months, U.A.W. organizers have been contacting workers at the Mercedes-Benz plant in Vance, Ala., with the hope that it might soon follow VW into the union fold.

In a news conference, Mr. King conveyed anger and bafflement at the results. He and his union thought they would win partly because Volkswagen, unlike most American companies, vowed to remain neutral and not oppose unionization.