A revolutionary new kind of television broadcasting may come later rather than sooner, if the leading TV networks have their way.

Broadcasters say they oppose a proposal by the chairman of the Federal Communications Commission that stations owned by ABC, CBS, Fox and NBC begin offering digital TV broadcasts within a year of receiving authorization from the government. Network representatives say they prefer a slower phase-in, stretching out as long as six years.

The FCC is widely expected to start the digital TV era next month when it formally gives station owners permission to use additional slices of the public airwaves, free of charge, for digital broadcasts. Digital broadcasting promises crystal-clear pictures and stereo-quality sound and could expand the number of channels available over the air six- fold.

The transition to digital TV, from the analog system that has been in place for more than 50 years, promises to be monumental for stations and viewers alike. It will require TV stations to buy new equipment and viewers to purchase new digital TV sets or attach converters to sets they have.

FCC Chairman Reed Hundt said the leading networks must begin offering their popular programs in digital format over their big TV stations relatively soon if the technology is to catch on with viewers.

To jump-start the transition, Hundt wants network-owned stations in the 10 largest U.S. metropolitan areas to begin digital transmissions by next year. Hundt reasoned that these stations - in places such as Washington, New York, Los Angeles and Chicago - are the industry's wealthiest and most widely watched and would be best able to afford new transmitters and equipment.

The FCC already has agreed to give every TV station in the United States additional portions of the airwaves to broadcast digital signals. The stations will maintain their analog broadcasts for several years so that viewers won't have to buy new sets immediately.

"No one is going to buy a digital TV set unless the major networks are broadcasting their programs in digital [format] in the major markets," Hundt said in an interview yesterday "It's a chicken-and-egg problem. We're asking [the net- works] to supply the chicken."

He called the granting of additional airwaves, which could be sold at auction for potentially billions of dollars, "a huge Christmas gift to the broadcast industry that they don't want to unwrap."

But broadcasters -- who have been critical of Hundt in the past for moving too slowly on digital TV and an even plusher cousin, high-definition TV -- now say Hundt is moving too quickly.

NBC's general counsel, Richard Cotton, said a host of uncertainties make it impractical to build digital TV facilities in only one year. For example, he said it's unclear how much it will cost to outfit each station because digital transmission equipment is still in the prototype stage. (Industry estimates range from $700,000 to $10 million per station, depending on the sophistication of the equipment).

What's more, he said, stations may not even be able to get zoning approvals from local governments within a year to erect new transmitters.

Cotton said six years, not one, "may be appropriate as an outside boundary" for stations to begin digital broadcasts. If they fail to do so by that time, he said, stations should lose the right to use the additional airwaves the FCC is awarding them.