He suggested that the case for interference-free television only must be made in Washington. "The rest of America, where the average American watches eight hours of TV per day, understands this issue quite clearly," Rehr said.

The dispute involves efforts by technology companies to harness dormant TV channels, known as white spaces, to provide broadband to unlicensed devices that would operate on the frequencies.

David Donovan, president of the Association for Maximum Service Television, another broadcaster group, emphasized that recent FCC testing indicates that even a small level of interference can freeze digital pictures. In addition, sensors on some prototypes could not always detect TV signals. "If you can't detect, you must reject," he quipped.

Representatives of ABC, Fox, NBC, public broadcasters, the digital TV set maker LG Electronics, and major sports leagues, including hockey, baseball and basketball, either participated or attended the press conference to show their support.

In a letter Monday, NAB endorsed FCC efforts to permit white spaces to be used for offering wireless broadband to stationary gadgets in rural areas. But it reiterated that mobile devices operating in the band would wreak havoc with DTV signals and make it impossible for affected parties to pinpoint the causes or locations of the interference.

Following the briefing, broadcasters headed for the FCC and Capitol Hill to appeal directly to FCC Chairman Kevin Martin, the other four agency commissioners and lawmakers.

"They're simply wrong on all accounts," responded Scott Blake Harris, counsel to the White Spaces Coalition. The group's members also include Dell, Hewlett-Packard, Intel and Philips Electronics. "These devices can be used successfully and will be used successfully," he said, adding, "The spectrum does not belong to the broadcasters and they are not licensed to use it."

Harris downplayed the FCC's findings, insisting that the agency demonstrated that at least one prototype works effectively and that sensors can be calibrated to avoid interference. His claims were backed by a report issued Monday by the New America Foundation.

At the press conference, LG Electronics spokesman John Taylor showed a tiny, portable digital television and said that in a few years, broadcasters would beam signals to similar devices, cellular telephones, laptop computers and personal digital assistants. Broadcasters dismissed suggestions, however, that they are seeking to warehouse unused TV spectrum so they can offer ancillary services over it years from now.