AN FRANCISCO, March 3 — The informal Wi-Fi networks that inexpensively provide wireless Internet access are fine, as far as they go — which is generally a few hundred feet. But what happens when there are enough of them to weave together in a blanket of Internet coverage?

What begins to appear is a high-speed wireless data network built from the bottom up, rather than the top-down wireless cellular data networks now being established by giant telecommunications companies.

Many Silicon Valley engineers now believe that it will be possible to take the tens of thousands of inexpensive wireless network connections that are popping up in homes and coffee shops all over the country and lash them together into a single anarchic wireless network. Connections could theoretically be passed from one Wi- Fi node to another, similar to the way wireless phone signals pass from cell to cell, thereby significantly extending the wired Internet.

Modeled closely on the original nature of the Internet, which grew by chaining together separate computer networks, the technology — known as wireless mesh routing — is being rapidly embraced in the United States as well as in the developing world, where it is viewed as a low-cost method for quickly building network infrastructure.

If the engineers are right, the popular and inexpensive Wi-Fi wireless standard, also known as 802.11, could serve as the wedge for the next-generation Internet, enabling a new wave of wireless portable gadgets that ultimately blanket homes, schools and shopping malls with Internet access.

Currently most 802.11 networks serve as individual beacons that provide wireless Internet connections to portable computers situated within 200 feet or so of an 802.11 transmitter. What wireless mesh routing offers is the promise of a vastly more powerful collaboration driven by the same forces that originally built the Internet.

"The good news is that broadband wireless access will finally explode," said Nicholas Negroponte, the director of the M.I.T Media Laboratory. "The social contract is simple: you can use mine when you are in the vicinity of Mount Vernon Street, Boston. But I want to be able to use yours when I am near you."

The technology is being driven both by a gaggle of ambitious start-up companies in Silicon Valley and elsewhere and by a hobbyist movement that mimics the original Homebrew Club that led to the personal computer industry.

Today, Tim Pozar and several of his friends are seizing the high ground, literally and figuratively, in a movement that could undercut the nation's cellular companies, which are investing tens of millions of dollars in top-down, heavily engineered, digital cellular networks.

Mr. Pozar, a radio engineer, is a member of the Bay Area Wireless Users Group, an active band of hobbyists who have been building free networks in communities through the region. Mr. Pozar and some of his friends have quietly begun obtaining the rights to place $2,000 wireless network access stations on the mountains and hilltops that encircle San Francisco Bay. If he succeeds, the network will be a starting point for a wireless data network that could eventually spread all over the Bay Area.

Significantly, what will set Mr. Pozar's planned Sunset Network and those like it apart from the commercial cellular networks now being constructed at great expense is that they will "self assemble" — expanding from one neighborhood to the next as individuals and businesses join by buying their own cheap antennas that either attach to the wired Internet or pass a signal on to another wireless node.

Mr. Pozar has even come up with a new acronym to describe his plan. In addition to the existing terminology of LAN's and WAN's — local and wide area networks — he is proposing the idea of NAN's, or neighborhood area networks.

The so-called Nanny Networks are rapidly becoming the hottest thing in Silicon Valley and internationally. There are now at least 19 companies developing proprietary wireless mesh routing technologies, all trying to replicate the original Internet in a wireless form.

It is not an easy task because the companies are engineering for a new kind of design, with which they must route data packets over paths where network nodes constantly pop up and disappear.

Moreover, wireless networks must overcome an array of environmental obstacles that do not plague wired networks, including hills, rain and trees.

Such networks, however, do have the critical advantage of economy of scale. In contrast to the cellular data networks, in which every customer is an added cost, in some respects in wireless mesh networks the more users who join the better the network performs.

In the jargon of Silicon Valley, wireless mesh routing is potentially a "disruptive technology," a new technology that is likely to upset the existing order by using the same powerful economics of cost and scale that initially drove the growth of the commercial Internet.

Already, companies like Mesh Networks, based in Maitland, Fla., are selling systems of wireless routers, making it possible to create self- assembling and self-healing networks that would cover an urban area.

There are also companies like Boingo Wireless and Sputnik, which focus on software and services that make it possible for wireless users to roam among networks. Similar technologies were crucial in the development of the original nationwide analog cellular voice networks.

In Silicon Valley, companies like Skypilot Network, FHP Wireless, Ultradevices, CoWave Networks, SRI's Packet Hop and others are all developing networks that have the potential to weave together networks made up of wireless antennas.

"We're going to start seeing more mom-and- pop Internet service providers buying access points that will support 802.11," Mr. Pozar said. "At first I thought it was going to just be geeks doing wireless, but now everyone has one of these things deployed."