By Michele Gershberg

NEW YORK (Reuters) - Google Inc will offer Internet developers an open system to create applications across Web sites, a move that could challenge the features behind the explosive popularity of social network Facebook.

Google's OpenSocial system gives developers standardized tools to build applications and embed them in many sites, eliminating the need for small startups or even one-person shops to customize their programs for each site.

It also has the potential to lure developers mostly allied with Facebook by allowing their applications to find a home on many other Web sites.

"This is about making the Web more social, how do you have your friends go along with you to any site on the Web?" said Joe Kraus, Google director of product management, in an interview.

Google said it had initially signed on about a dozen partners, including social network LinkedIn for business professionals, its own Orkut network and Friendster.

Developers who are testing the program include key companies behind Facebook applications, such as music recommendation service iLike and Slide, which created the "Top Friends" ranking application.

Industry blogs have speculated for nearly a month that Google aimed to unleash a major challenge to Facebook, whose decision to open its site to developers in May helped it grow to more than 48 million users.

Facebook, which secured an investment from Microsoft Corp. last week that values it at $15 billion, is due to announce its own new advertising strategy on November 6.

Google had also been interested in a partnership with Facebook as it competes more closely with Microsoft for drawing Web audiences and advertisers.

Developers briefed on OpenSocial said it will help them seek the widest distribution possible for their applications, some of which are already used by millions of people on social networks.

"For months we've been approached by other Web sites that want us to build iLike widgets for them and we've been unable to build it for them," said iLike Chief Executive Ali Partovi. "The benefit OpenSocial offers us is we can essentially ... syndicate what we do to other social networks."
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