Federal regulators are stepping up their pressure on television stations to give up billions of dollars worth of airwaves in major markets around the country, saying the spectrum is urgently needed by local public safety officials.

Seizing on a conclusion of the 9/11 Commission Report, Congress and the Federal Communications Commission are using the limits of the nation's emergency communications system to try to kick-start the process of converting television broadcasters from analog signals to digital ones.

The conversion would free large segments of the broadcast spectrum for emergency services in major metropolitan areas. The 9/11 Commission concluded that emergency communications were crippled by the sudden spike in cell phone calls in the hours immediately after the terrorist attacks, and it called on Congress to pass legislation that would take some of the spectrum back from broadcasters.

The conversion from analog to digital is supposed to be well underway already. In 1996, Congress granted television stations second channels for digital service in return for their promise to surrender the portion of the broadcast spectrum on which analog signals operate. That would allow the government to turn parts of the spectrum over to local emergency authorities and auction the rest to wireless companies or other investors.

The analog spectrum is worth an estimated $70 billion.

The process has been slowed, however, by consumers not replacing their old analog sets with expensive new digital televisions as quickly as had been hoped.

Concerned about the lag, some members of Congress have proposed that the government simply seize by Jan. 1, 2007, the signals of about 75 local broadcasters that use channels 63, 64, 68 and 69 -- the frequencies that would be most convenient for public safety officials. Another proposal, backed by the FCC, would set a deadline of 2009 for all broadcasters to give up their analog channels. While that is technically a two-year extension of the current law, the new proposal would make it difficult for the broadcasters to further delay the turnover.

The debate over the TV signals is the latest example of the federal government's struggle to balance national security needs against high costs and public inconvenience.

Broadcasters say, in this case, that millions of viewers who don't own digital television sets would lose access to free broadcast service if the analog channels are reclaimed too soon.

Broadcasters lobbied Congress for more than a decade to get the digital channels, saying the survival of free, over-the-air television depended on their ability to have a digital signal that could compete with satellite and cable offerings.

The extra channel allows broadcasters to offer high-definition pictures and better sound and even allows stations to air up to six different signals at the same time.

Once a station turns off its old analog channel, only those homes that have acquired a new digital TV or subscribe to a premium cable or television service will be able to pick up the local signal.

The National Association of Broadcasters "recognizes the importance of public safety officials communicating during emergencies, and we're working with Congress and the FCC to develop appropriate DTV [digital television] timelines that don't disenfranchise viewers from local television," said Dennis Wharton, a spokesman for the broadcasters trade organization.

Congress originally set a deadline for the broadcasters to give up their analog channel by Jan. 1, 2007. The legislation included a caveat, however, that effectively rendered the deadline meaningless by allowing broadcasters to keep both channels if fewer than 85 percent of the homes in a station's market could not receive a digital signal.

At a Senate hearing this week, Lowell W. Paxson, chief executive of Paxson Communications Corp., called the legislation to take channels by 2007 an "illegal taking of our rights." He said that if the bill becomes law, broadcasters will fight it in court.

Federal officials are not the only ones interested in dislodging the broadcasters from the analog spectrum. Technology companies are also eager to get their hands on the airwaves, most of which are expected to be sold at a government auction, and have been quietly lobbying Congress and the FCC to keep the pressure on the broadcasters to give up the channels. Intel Corp., the world's largest computer chipmaker, is also interested in some of the spectrum now controlled by the stations between channels 62 and 69. Intel argues that the spectrum could be used to expand the reach of high-speed Internet services. "We think this spectrum would be ideal for wireless broadband uses such as WiMax," said Peter K. Pitsch, Intel communications policy director.

WiMax is a nascent technology that allows users to more universally access the Internet over wireless connections. Intel views WiMax as a potential growth market for its chips.

The strength of the signals would allow the owners of the airwaves to transmit data to personal computers and palm-sized computers at relatively low costs, Pitsch said.