WASHINGTON -- Federal television regulators are circulating a plan that would turn off the analog TV signal the nation has used since electronic TV was first broadcast in the late 1930s before the end of the 21st century's inaugural decade.

Under the plan, broadcasters would be required by 2009 to return the analog frequencies they use and switch to digital television because the FCC will have certified that at least 85% of the nation's television audience is receiving digital TV signals, commission officials said Wednesday. Broadcasters are supposed to give back the analog frequencies at the end of 2006 or when the audience capable of receiving a digital TV signal reaches 85%, whichever comes first.

Congress and the FCC, however, never determined exactly how to measure that 85%. FCC mass media bureau chief Ken Ferree said the plan is a way to make the switch as painless as possible but still get broadcasters to give up the analog frequencies.

"They'd rather eat their children than give up their spectrum," he said. "I would do the same thing."

Broadcasters' must-carry rights would flip from the analog signal in broad use now to the digital TV signal most broadcasters have begun to use. Broadcasters could then choose whether a cable system would be allowed to carry the signal on its analog or digital tier. If the signal is carried on the analog tier, cable systems would have to down-convert the signal for those sets unable to carry it, but those people would be counted as part of the digital TV audience.

Cable customers on the digital tier would receive broadcasters' digital signals, and as more and more digital TV sets come into the market, more people will opt for the digital tier, Ferree believes.

A de facto hard shutoff date of 2009 -- a market mechanism automatically built into the plan -- will help the switch, he said.

"If you're a weak station, you're going to elect to go analog because the analog (tier) gets everybody," he said. "Now, that's for the weakest of the weak broadcasters."

The scenario is different for large, powerful networks because they generally work out carriage issues with the cable operators. But medium-sized stations or big independents might gamble and choose to be carried on the digital tier, Ferree said.

"For the strongest of the strong, it probably doesn't matter because they're going to negotiate all this carriage anyway," he said. "What happens for middle-tier broadcasters that maybe today are trying to do some high-definition programming but aren't getting carriage on many cable systems ... that broadcaster may say: "Look, I can sort of roll the dice. I can turn in my analog and elect true digital carriage. ... I'm going to bet that the cable operator is not going to take me off the analog because he's not going to want to alienate his viewers.' "

Cable operators would have an incentive to switch everyone over to a digital system because it would free up bandwidth on their systems that is getting eaten up by analog broadcasts, he said, and that bandwidth can be used for other services.

While there is no formal document, the commissioners have all been briefed at least once on the plan, as have congressional staffers. Ferree said the idea has been generally well-received, and he hopes to begin work on a final bureau document almost immediately. Once that plan is finished, the commission would then get a chance to approve, reject or rework it.

Cable industry officials and TV set makers declined to comment on the plan late Wednesday, saying they want to see the details. But broadcast industry executives blasted the plan.

"We appreciate the suggestion that 2009 is a more realistic date for completing the DTV transition," National Association of Broadcasters spokesman Dennis Wharton said. "NAB remains concerned that the Ferree initiative is simply a spectrum-reclamation plan that would strand both consumers and broadcasters who have collectively spent billions embracing the best television technology on the planet."

The NAB has a particular problem with the idea that cable systems could down-convert a broadcaster's digital signal, saying that it "makes a mockery of 15 years of government-industry partnership in advancing the digital transition."

Wharton said the plan should be "immediately rejected."

"The notion that cable companies could down-convert DTV signals to analog -- and count those customers toward the 85% DTV penetration test -- would seriously hinder the transition to digital and high-definition television," Wharton said. "A fundamental question is this: How would allowing a cable operator to degrade a local broadcaster's high-quality HDTV signal into analog further the DTV transition?"

The plan also has a weak spot in that it leaves open the question of what gets done with the 15% of the nation that does not pay for cable or satellite TV. Under Ferree's plan, cable and satellite TV subscribers would not notice the switch, but on Jan. 1, 2009, sets that get their signals with an antenna would cease to function.

"Everyone wants these TVs to work," Ferree said. "Not only are these 15% consumers, but they are voters. Nobody wants these folks to go dark."

Ferree suggested that the government might have to help some of those people out. Since most of that 15% would be the poor, a subsidy to buy a set-top box that would convert the signal might be one way to go, he said. That $1 billion-$2 billion cost could come out of the proceeds that an auction of the analog frequencies would raise. While estimates for that sale have gone as high as $70 billion, Ferree believes that a more accurate number would be around $50 billion.

"It's certainly a much smaller cost than the auction will bring in," he said.

While the transition to digital TV has been going on for years, Ferree said it was time to come up with a plan to make the change at a certain date. The rest of the world is switching over to digital TV signals, and the public policy reasons for allowing broadcasters to essentially "warehouse" the analog frequencies is being outweighed by the need for frequencies by public safety agencies and the new services that could be generated once those channels are released, Ferree argues.

"The rest of the world is doing this, and if we want to sit on our spectrum to save it for the TV you take to the Redskins game to make sure it works, well then forget it," he said. "My kids will have died by the time it happens."