WASHINGTON — Attention owners of primitive TVs: If you still use an antenna to watch "American Idol," your picture will disappear at midnight on Feb. 17, 2009, unless you buy something called a digital converter box.

No one knows how much these boxes, which have yet to be produced, will cost. But the government will help you pay for them, at least until the money runs out.

The reason millions of TVs will be rendered obsolete is a government mandate for broadcasters to convert their signals from old-style analog to new-style digital.

The agency responsible for overseeing distribution of the converter boxes, the National Telecommunications and Information Administration, explained yesterday how the program is supposed to work.

Every household, regardless of whether it needs a box, will be eligible to receive two coupons worth $40 each that can be used to buy two converter boxes. The coupons must be requested between Jan. 1, 2008, and March 31, 2009.

Congress, in the Deficit Reduction Act of 2005, set aside $1.5 billion to pay for the coupon program. Initially, $990 million will be used to pay for coupons and cover administrative costs — capped at $110 million.

An additional $510 million may be allocated, but those coupons are reserved for households that only have over-the-air television.

The massive conversion is designed to make better use of the public airwaves. Digital broadcast signals take up less spectrum, so once broadcasters make the transition, it will free up a big chunk of the airwaves and allow the government to auction it off and dedicate some of it to public safety.

The Federal Communications Commission says that as of June 2005, there were 15.4 million television households in the U.S. that received over-the-air signals only. Add to that homes that receive cable or satellite, but also have sets that rely on antennas, and the number gets larger.

And then there's cable.

The National Cable and Telecommunications Association reports that roughly 66 million U.S. households subscribe to basic cable. About 32 million of those have digital cable, and sets hooked up to that service will not be be affected by the change. Anyone who receives direct broadcast satellite signals also has nothing to worry about.

That's where it starts to get complicated.

For consumers who plug the cable right into their cable-ready TV sets, they will either be provided with a set-top box by their service provider, or the provider will send an analog signal to its customers. But the issue has not yet been fully resolved. In any case, cable-only channels won't be affected during the transition.

Despite the uncertainty, the affected industries are bullish on the program. A coalition consisting of the National Association of Broadcasters, the Consumer Electronics Association and the Association for Maximum Service Television (a local television station trade group) praised the new rules.

In a statement released 30 minutes before yesterday's press event, and before the rules were actually made public, the group stated they would "provide much-needed certainty to broadcasters, manufacturers, retailers and ultimately the American public."