MOUNTAIN VIEW, California (Reuters) - Google Inc is challenging Microsoft Corp with its own Web browser that lets users run many applications that once worked only when installed on local PCs, executives said on Tuesday.

Google introduced a public trial version of its new browser software, Chrome, which is designed to handle not just text and graphics, but more complex computer programs.

Chrome, available in 43 languages in 100 countries at www.google.com/chrome, has been designed to download software and Web pages faster than existing browsers. It even allows users to keep working when one of its windows crashes.

This represents Google’s long-anticipated head-on attack on Microsoft and its Internet Explorer, which has three-quarters of the Web-browsing market. Google has backed Mozilla Corp’s Firefox browser, which holds about 18 percent of the market.

Google engineers and executives call Chrome a “fresh take on the browser,” a 15-year-old technology that is supplanting 25-year-old desktop software as the basic way users interact with computers.

“You actually spend more time in your browser than you do in your car,” said Brian Rakowski, group product manager for Google’s browser project.

Chrome was seen by analysts as partly a defensive move due to Google’s fear that the recently upgraded Internet Explorer 8 (IE 8) could be used to lock out Google. Google’s core business of Web search and related advertising depends on browsers.

A Microsoft executive said IE 8 gives users control over how and where they navigate, improves their day-to-day browsing experience, and keeps people safe from new security threats.

“Microsoft understands that Web browsing is crucially important for hundreds of millions of people, which is why we invest in Internet Explorer so heavily,” Dean Hachamovitch, general manager of Internet Explorer, said in a statement.

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CHALLENGE TO MICROSOFT WINDOWS?

Google co-founder Sergey Brin said Chrome was designed to address the shift to using software from within a Web browser rather than as locally installed computer applications running inside Microsoft Windows or some other operating system.

“I think operating systems are kind of an old way to think of the world,” Brin told a group of reporters after the news conference at Google’s Mountain View, California headquarters. “They have become kind of bulky, they have to do lots and lots of different (legacy) things.”

Google believes any task done in a standalone desktop computer application can be delivered via the Web and Chrome is its bet that software applications can be run via a browser.

“We (Web users) want a very lightweight, fast engine for running applications,” Brin said.

“The kind of things you want to have running standalone (on a computer) are shrinking,” he said, adding that he still edits photos on his computer rather than using a Web program.

GOOGLE BORROWS FROM APPLE, FIREFOX

Chrome borrows liberally from other browsers running open-source software code, including Apple Inc and Firefox, and company officials said they planned to fully share Chrome code with other developers.

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“We have borrowed good ideas from others,” Google Vice President of Product Management Sindar Pichai said. “Our goal here was to bring our point of view, but do it in a very open way.”

Because Chrome relies on Apple’s open-source WebKit software for rendering Web pages, it can run any application that runs on Apple’s Safari Web browser, Pichai said.

“If you are a webmaster, and your site works in Apple Safari then it will work very well in Google Chrome,” he said.

Greg Sterling, a Web analyst with Sterling Market Intelligence, said Google’s entry into the browser market has echoes of the bruising “browser wars” of the late 1990s, when Microsoft crushed Web pioneer Netscape Communications.

But while the competition between Microsoft and Google is likely to produce many improvements for consumers, the likely fallout from the battle will be other browser makers that have only recently begun to pry market share away from Microsoft.

Sterling said Firefox could become a victim of “friendly fire” from Google as many of its users are the same early adopters who are most likely to switch and try a new browser.

“Firefox has softened up and paved the way for Google. Without Firefox, Chrome would not be possible,” Sterling said.

Brin said Google planned to continue to work closely with Mozilla, whose primary financial backing has come from Google in recent years. He said he hoped to see future versions of Chrome and Firefox become more unified over time.

Chrome organizes information into tabbed pages. Web programs can be launched in their own dedicated windows.

Among Chrome’s features is a special privacy mode that lets users create an “incognito” window where “nothing that occurs in that window is ever logged on your computer,” according to a Google promotional guide.