Federal agents targeting illegal immigrants raided meatpacking plants in six states yesterday, arresting hundreds of workers on the uncommon charge of identity theft and shutting down the world's second-largest meat processing company for much of the day.

About 1,000 U.S. Immigration and Customs Enforcement agents with search warrants entered plants owned by Swift & Co., of Greeley, Colo., charging that "large numbers" of workers illegally assumed the identities of U.S. citizens or legal residents by using their Social Security numbers to get work, ICE officials said.