In a deal estimated to cost $100 million a year for five years, Howard Stern, one of the most popular personalities in radio, has signed a contract with the Sirius Satellite Radio Company and will leave his longtime home on Infinity Broadcasting starting in January 2006. The $100 million figure covers production and operating costs for the Stern show, according to a statement by Sirius. Mr. Stern said in a telephone interview today that his decision was driven both by a desire to help build satellite radio, which is unregulated by the federal government and mostly free of commercials, and by the need to escape what has become ever-increasing restrictions on the content of his program. Numerous radio stations that carry Mr. Stern's show have been fined heavily by the Federal Communications Commission over sexual and scatological references on the show. A number of stations owned by Clear Channel Communications dropped Mr. Stern's show over the continuing problems with the F.C.C.