WASHINGTON — As new high-definition televisions fly off store shelves, millions of old sets soon could be flying into the trash.

A major change to broadcast television in 2009 — the conversion from analog signals to all digital — is expected to send many Americans to the store for new TV sets. That could mean a flood of outdated TVs, which contain lead-encased picture tubes and other hazardous material, heading into landfills.

"There's going to be an e-waste tsunami that hits America," said John S. Shegerian, chief executive of Electronic Recyclers in Fresno, California's largest electronics recycler.

Lawmakers and environmentalists already are concerned about the amount of technology waste — laptops, iPods, printers and other gear — in dumps.

So far, TVs have been less likely to end up in landfills than other electronics, recycling experts say. Although cell phones, computers and other gadgets generally get thrown out or given away when people upgrade, TVs tend to hang around the house if they still work. They're used to play video games or to watch DVDs, or they get plugged into the cable system or hooked to rabbit ears to serve as an extra set.

The latest U.S. Census figures indicate that the average household had 2.5 television sets in 2004, a 25 percent increase since 1990. In all, there were 268 million TV sets.

"There's a lot of different uses," said Parker Brugge, environmental counsel for the Consumer Electronics Association. "That's why the number of televisions in consumers' households keeps going up."

But the calculus that leads Americans to hang on to old TVs could change Feb. 18, 2009.

That's the day a federal law will require all TV stations to start broadcasting only in digital. Tens of millions of old analog TVs will need to be hooked to a cable or satellite box, or fitted with a special converter, to display the new signals.

"That conversion is going to trigger the reality that even if it's working, even if I turn it on and the screen lights up, this is a device that's incompatible with the current technology," said Mark Murray, executive director of Californians Against Waste, a Sacramento-based environmental group focused on recycling. "I do think we'll see a wave of new discards."

How big a wave is unclear. The federal Environmental Protection Agency has not made any projections, and the California Integrated Waste Management Board is studying the issue.

"There is going to be an impact, but what the full extent is we're not entirely sure," said Lanny Clavecilla, a spokesman for the state board.

Consumer electronics manufacturers are trying to stem environmental fallout. As part of its effort to inform the public about the digital TV transition, the Consumer Electronics Association has touted its recycling Web site, www.mygreenelectronics.org, which helps people find places to drop off old TVs and other devices.

According to a survey last year by the trade group, 19 percent of people threw their old electronics in the trash. The rest either gave them away (55 percent), recycled them (18 percent) or sold them (7 percent).

Shegerian, the recycler in Fresno, says the number of discarded TVs can only increase, as prices on flat-panel TVs drop and the digital conversion leads more people to upgrade.

"You have a new influx of televisions coming into the solid waste stream," he said.

The Fresno facility processes more than 5 million pounds a month from municipal and private collection sites. Partly because of the anticipated growth in discarded analog TVs, the company expanded to Massachusetts and expects to open facilities in 10 other states in the next 18 months.

The EPA says older sets contain a host of hazardous materials. Most states ban leaded cathode ray tubes — the technology used to power those TV sets — from landfills.

Cathode-ray tubes are encased with leaded glass to block harmful X-rays created in the picture-making process from escaping. The average picture tube contains 4 pounds of lead.

There are lead solder and cadmium in circuit boards, mercury in switches and brominates in flame retardants used on plastic casings. If dumped into landfills, those materials could seep into underground water.

Next-generation TVs — plasmas and liquid crystal displays — don't use cathode-ray tubes to display pictures.