SAN FRANCISCO — Google Inc. yesterday showed off a cell phone that could provide the first real challenge to Apple Inc.'s iPhone: a mass-market device with a sharp touch screen and slide-out keyboard that brings the experience of mobile Web-surfing closer to that of a personal computer.

When it goes on sale in U.S. stores Oct. 22, the $179 G1 from HTC Corp. will be the first of many expected gadgets, from a variety of manufacturers, to run Google's new mobile operating system and have many of the Internet giant's services built in.

The G1, which works on the T-Mobile USA network, marks another salvo in the cell phone wars as tech titans try to upend the wireless market to seize a major business opportunity.

The likes of Google, Apple and Microsoft Corp. are betting they can make billions of dollars by selling software and delivering ads to a new generation of powerful mobile gadgets.

"The cell phone is the world's most popular device, and it is going to be the world's most popular way to access the Web," NPD group analyst Ross Rubin said.

For these tech giants, staking a claim on the mobile Web is a matter of self-interest and preservation. Cell phones outnumber personal computers roughly three to one.

When it comes to connecting people to the Web, cell phones still lag far behind. But the iPhone, BlackBerry and other so-called smartphones are changing that, keeping their owners connected anywhere. Research firm IDC predicts that by 2012, more mobile devices than computers will be surfing the Web.

Those gadgets could become lucrative vehicles for selling ads, especially ones targeting cell phone owners with shops and services near their precise locations.

Google executives predict the company will eventually make more money on the mobile Web than on the traditional Web. Investment bank Collins Stewart says it expects the search giant to add $5 billion in revenue from cell phone ads by 2011.

The G1 connects to Wi-Fi hotspots, features a keyboard and trackball and has such features as a built-in compass, so when a user looking at Google Maps turns, the image does too.

But analysts say HTC and T-Mobile lack the marketing firepower for the G1 to conquer the smartphone market. The BlackBerry, made by Research in Motion and supported by all the major wireless carriers, dominates the corporate part of the market, while Apple's iPhone, which runs on the AT&T network, has quickly become a consumer hit.

But Google, based in Mountain View, Calif., hopes it's just the beginning. Manufacturers such as Samsung and Motorola Inc. are also working on phones that run Google's Android operating system for carriers such as T-Mobile and Sprint Nextel Corp. Sprint and China Mobile were supposed to launch Android phones in coming months but hit delays.

"We set out to build Android so that we could enable a lot more people to access the Internet," said Andy Rubin, Google's senior director of mobile platforms. "We want to make the entire Web experience as good as possible on the small screen."

T-Mobile, the No. 4 U.S. carrier, raced to become the first provider to release a Google-powered phone to help it better compete against market leaders AT&T, Verizon Wireless and Sprint. "We tried to build a mass-market device that is affordable to consumers," said Cole Brodman, T-Mobile's chief technology and innovation officer. "We think it has got universal appeal."

If Brodman is right, "Android could be a threat to all," said Needham & Co. analyst Charlie Wolf.

Apple launched the iPhone in June 2007. In addition to making calls, the iPhone lets consumers send and receive e-mail and instant messages, play music and videos and surf the Web. And iPhone owners can check their bank accounts or decide on a movie at the beach.

Brent Bushnell recently landed in Boston and jumped on a train without thinking. He pulled up the map on his iPhone to figure out where he was headed and find his hotel. "I boot-strapped my way without missing a beat," he said.