"This is going to bring the internet into cell phones in a very cool way," Andy Rubin, Google's director of mobile platforms, told the Associated Press news agency.

Mr Rubin's firm, called Android, was bought by Google in 2005 and the software it developed forms the basis of the new stack.

Google has formed the Open Handset Alliance (OHA), made up of 34 companies, including chip manufacturers and handset makers.

The move will be seen as a major competitor to Microsoft, Research in Motion, Palm and Symbian, who make the leading software systems for mobiles.

Google's Android software will be provided to handset makers free of charge and could lead to a price war for operating system licenses and potentially cheaper handsets.

In the United States mobile networks such as Sprint Nextel and T-Mobile will carry the Google-powered phones.

'Unleash potential'

China Mobile, Telefonica in Spain and Telecom Italia are among the carriers that have signed on to provide services outside the US.

"This partnership will help unleash the potential of mobile technology for billions of users around the world," Eric Schmidt, Google's chief executive and chairman, said in a statement.

Rene Obermann, chief executive of Deutsche Telekom, said Android would offer a "better than internet experience for mobile users".

"This is a shot that is going to be heard around the world, but it's just the first shot in what is going to be a very protracted battle in the next frontier of the mobile web," said analyst Michael Gartenberg, at Jupiter Research.

In a call to reporters, Mr Schmidt said: "We want to create a whole new mobile experience for users.

"Mobile users want the same applications on the phone as they use on the internet."

Peter Chou, chief executive of HTC, said the agreement to join the OHA did not mean the firm would stop the use of other operating systems on its platforms.

"We do have commitments with some carriers and will continue with those lines," he said.

There have been many reports of a so-called Google phone in recent months.

"Today's announcement is more ambitious than any single Google Phone that the press has been speculating about over the past few weeks," said Mr Schmidt.

"Our vision is that the powerful platform we're unveiling will power thousands of different phone models."

But Mr Schmidt would not rule out the release of a Google Phone in the future.

Adam Leach, principal analyst with Ovum, said: "It's an important announcement. That number of companies already committing to the service is very impressive."

Mr Leach said the danger was that the move would create "yet another" competing service and not a "truly open platform".

"We've seen collaboration of this sort before in the mobile industry and there's quite a number of platforms already out there professing to remove fragmentation, speed-up time to market and enable third-party innovation.

"The proposition from that point of view is not new."

He added: "This doesn't seem to be a beta release of a technology. If I were a competitor, I would be sitting up and paying attention."

Google's system will be based on computer code that can be openly distributed among programmers, allowing them to build new applications.

A development tool kit for working on the new platform will be released next week.