Call it a government bait-and-switch. The victims: three communications companies that stand to lose freebies worth some $500 million each. In 1991, the FCC came up with a sweetener to spur development of technologies for a new wireless phone service called PCS--a free license and the market of choice to service-providers. Last year, these "pioneer preferences" were tentatively awarded to Cox Communications, which chose Los Angeles; American Personal Communications, which picked Washington, and Omnipoint, which selected New York. But powerful House Commerce Committee Chairman John D. Dingell (D-Mich.) wants the FCC to renege on the deals because the licenses are too valuable to give away. The FCC is expected to let the companies keep the licenses--if they pay the market value.