The move marks a significant win for backers of the new technology, such as Intel Corp. and Motorola Inc., while it would be a setback for wireless pioneer Qualcomm Inc, which is behind a rival technology.

WiMax is a technology that can spread a wireless Internet signal over several miles, a long-range version of the popular short-range wireless Internet technology, Wi-Fi, found in airports, coffee shops and many homes.

Analysts say building a nationwide WiMax network could cost Sprint between $1 billion and $4 billion, a hefty sum for a company that is already struggling to meet Wall Street's expectations. Sprint said it expects to invest $1 billion on the project in 2007 and between $1.5 billion and $2 billion in 2008.

Sprint's decision carries considerable risks: Investors have hammered telecom companies that have made large capital investments in new technologies, banking on future markets to emerge. For example, among other things, Verizon Communications Inc.'s stock has been under fire as the company is rolling out a costly new fiber optic network that it says will position the company to deliver a bundled TV, Internet, and phone service. Also, WiMax technology is still untested on a large scale.

Sprint is making a huge bet that consumer demand for wireless Internet access and services such as cellphone downloads of music and video will continue to grow in the coming years. Consumers already can get access to wireless Internet service at Wi-Fi "hotspots" in airports and coffee shops, and some cities, like Anaheim, Calif., are blanketing their terrain with Wi-Fi connections.

But the service isn't available everywhere and sometimes has patchy reception. Cellphone companies, including Sprint, are rolling out cellular Internet service, but those networks also have their limitations -- they aren't designed to handle massive amounts of traffic and downloading activity.

Sprint had previously said it planned to build a new wireless network, but did not decide on a new technology until recently. The company said in the past that such a network would be designed to accommodate heavy data-usage activities like video streaming on cellphones and laptops without clogging up the cellular networks people rely on for phone calls.

In an interview last week, Atish Gude, Sprint's senior vice president of corporate strategy and development, said the company wants to tap into an entirely new market by eventually connecting consumer electronics devices such as videocameras and MP3 players to the Internet for the first time. "We intend to light up a whole category of consumer electronics devices that aren't lit up," Mr. Gude said.

Intel has been the most prominent champion of WiMax. The company previously included Wi-Fi in its chipsets as a way to boost purchases of laptops. Now it has switched its attention to WiMax, hoping to generate yet another cycle of computer purchases and satisfy consumer demand for broader-range mobile Internet access. The company was at the forefront of efforts to develop the set of specifications equipment makers will use to process