With millions of U.S. viewers still apparently unprepared for the nation's switch to digital TV, nearly 500 full-power television stations across the nation are preparing to move ahead with the transition and drop traditional over-the-air broadcasts next Tuesday. The loss of signals in those markets means that some viewers will no longer get television reception unless they have installed a digital converter box and, in some cases, purchased a new antenna. Nielsen Co. has estimated that 6.5 million over-the-air households are unprepared for the "digital transition." Elderly, Latino and low-income households are believed to be most affected. "If we have a serious natural disaster and folks don't have a TV on which to receive updates, that's a problem," said Christopher Murray, Consumers Union senior counsel.None of Washington's stations asked to begin their transition next week, according to the Federal Communications Commission. In Baltimore, WBFF (Channel 45) and WNUV (Channel 54), have asked to make the switch. Consumer advocates have warned for months that the sudden loss of television service poses a threat to public safety because so many people receive warnings by television. Stations moving ahead with the digital transition were required to notify the FCC by this past Monday night. The agency must give its approval for stations to halt analog signals. Subscribers with cable or satellite TV service, who represent about 85 percent of households, or those with digital receivers are not expected to be significantly affected. Some small cities, such as Burlington, Vt., and South Bend, Ind., will see traditional over-the-air broadcasts almost come to a halt next week, if the FCC grants stations' request; others, such as Dayton, Ohio; Mobile, Ala.; Madison, Wis.; Lincoln, Neb.; Fort Myers, Fla.; and Macon, Ga., will see most stations end analog broadcast signals, if permission is granted. Most of the affected stations are in smaller markets, but together cover millions of viewers. The onset of the digital transition comes despite Congress's best intentions to delay it. Last week, Congress lifted the Feb. 17 deadline for stations to drop the old signals, postponing it until June. Lawmakers explained that despite years of planning, the $1.5 billion federal program to aid consumers during the switch has been underfunded and overwhelmed. A program that offered consumers $40 coupons to buy converter boxes reached its budget limit last month, leaving the requests for more than 3.7 million coupons on a waiting list. It will be months before they can be delivered to consumers. But while Congress has postponed the long-standing February deadline, hundreds of stations have been preparing to move ahead anyway. Some station officials explained that they've already scheduled the crews to make the switch; others said their budgets didn't allow for continuing transmission of the analog signal.