LAS VEGAS - The future of the Internet promises the ability to download huge files - a full set of encyclopedias, for example - in a few minutes that previously would have required hours or weeks to transfer, Comcast Corp. chief executive officer Brian L. Roberts said yesterday.

Roberts introduced the next generation of cable modems to the public for the first time at a presentation at the National Cable and Telecommunications Show here. The so-called wideband modems will allow users to download content - movies, songs, photos - at speeds of 100 megabits or more per second, Roberts said. That is about 20 times faster than current cable-modem speeds.

Verizon Communications Inc. advertises speeds of about 5 to 30 megabits per second - depending on the price package - for Internet downloads on the FiOS fiber-optic system it is now rolling out.

As the audience watched, Roberts downloaded the Encyclopaedia Britannica and a Merriam-Webster dictionary - in a little more than three minutes.

Roberts said he expected the new technology to lead to a wave of innovation.

"I think we're in a great position to create a new platform and let all these entrepreneurs figure out what to do with it," he said.

Cable companies are not saying how long it will take for this new technology - known as DOCSIS 3.0, which stands for "data over cable service interface specification" - to reach the public. It is being developed by CableLabs, an industry consortium.

Roberts' presentation is part of a larger theme at this year's Cable Show: Cable companies are trying to prove that they will remain competitive in an era where they face new competition from phone companies offering TV and from start-ups offering Internet video.

He compared his demonstration yesterday to one from the 1996 Cable Show, when he demonstrated new cable modems against phone companies' dial-up technology. Since then, both phone and cable companies have boosted speeds dramatically, allowing for the creation of new companies and technologies, he said.

"At the time of the first demo, Google didn't exist, and Amazon wasn't a public company," he said.

Roberts and others at yesterday's panel argued that cable's superior technology would enable them to navigate successfully around the competition - and even benefit from it.

Philippe Dauman, president and chief executive of Viacom Inc., which operates such channels as MTV and Comedy Central, said his company had found that Internet video, rather than displacing its cable channels, reinforces them.

"It's not duplicative of what's showing on Brian [Roberts] and Dick's [Time Warner chief executive Richard Parsons] cable systems," Dauman said. "It's additive. We used to fight with Time Warner and Comcast over [programming] rates. Now, we're engaged in how can we deepen the customer relationship."

Parsons said investors' fear that start-ups would topple giant companies such as Time Warner and Comcast reminded him of his playground days, when the smaller kids were better athletes because they could control their bodies more easily than bigger children like him. His mother always told him that he simply needed to grow into his body, which he did.

"The notion," Parsons said, "that the new kids on the block are taking over, I think, is a false notion."