Is high definition video over IP going to bring down the Internet (and your phone calls)? (No.)

Every day, it seems, a new service pops up offering to send you video over the Internet. "Desperate Housewives," Stephen Colbert heckling the president, clips of bad dancers at wedding parties: It’s all there.

You may be up for it, but is the Internet?

The answer from the major Internet service providers, the telephone and cable companies, is "no." Small clips are fine, but TV-quality and especially high-definition programming could make the Internet choke.

Most home Internet use is in brief bursts — an e-mail here, a Web page there. If people start watching streaming video like they watch TV — for hours at a time — that puts a strain on the Internet that it wasn’t designed for, ISPs say, and beefing up the Internet’s capacity to prevent that will be expensive.

To offset that cost, ISPs want to start charging content providers to ensure delivery of large video files, for example.

Internet activists and consumer groups are vehemently against those plans, saying they amount to tilting the Internet’s level playing field, one of the things that encourages innovation. They want legislation to guarantee a "neutral" Internet, but prospects appear slim.

At the heart of the debate is a key question: How much would it really cost the Internet carriers to provide a couple of hours of prime-time TV over their networks every day?

The carriers are playing their cards fairly close to their chest, but there are ways to get close to an answer.

One data point: As a rough estimate, an always-on, 1 megabit-per-second tap into the Internet backbone in downtown Atlanta, bought wholesale, costs an ISP $10 to $20 a month, according to the research firm TeleGeography Inc. An ISP’s business is carrying data from that tap to the customer.

One megabit per second doesn’t sound like that much, but ISPs spread that bandwidth out over their subscribers. Analysts estimate that ISPs sell around 30 times more bandwidth to their end users than they can connect simultaneously to the Internet (the figure probably varies widely from provider to provider).