Google's OpenSocial got a major boost on Thursday when MySpace, the world's most popular social networking site, announced it will participate in the project to streamline the creation and adoption of social Web applications.

This means that MySpace, like other OpenSocial participants, will be able to offer all applications created by third-party developers that are compatible with the OpenSocial API.

For developers, the addition of MySpace to OpenSocial is a major step, opening their applications to that social networking site's massive base of users.

On Tuesday, Google confirmed the existence of the OpenSocial program, which is widely seen as not only Google's strongest move in social networking to date, but also as a response to the rising popularity -- and threat -- of Facebook.

Although Facebook is the second-most popular social networking site in the world, it is growing faster than MySpace, thanks in large part to the fact that Facebook opened its platform to external developers in May, something MySpace is now only about to do.

To date, Facebook has about 7,000 applications available for its members. It hasn't said whether it will participate in OpenSocial, although Google says the door is open.

"Despite reports, Facebook has still not been briefed on OpenSocial. When we have had a chance to understand the technology, then Facebook will evaluate participation," Brandee Barker, Facebook spokeswoman, said.

OpenSocial can, in theory, dilute this distinguishing feature of Facebook by offering a core set of APIs that will let developers write an application once that is compatible with multiple sites.

In other words, OpenSocial seeks to address the inconvenience for developers of having to port applications to different social networking Web sites.

In addition to MySpace, other partners participating in OpenSocial include Oracle, Salesforce.com, Hi5, iLike, LinkedIn, Slide, Ning, Friendster, Six Apart, and Plaxo.

The recent furor over Facebook, MySpace, and Google's OpenSocial is indicative of the rising importance of social networking sites for people both in life and at work.

Originally considered of interest only to teens and young adults for communicating with friends, these sites have broadened their demographic appeal as they have proven useful for more activities, including professional networking and business activities.

For Google, which has had the Orkut social networking site for several years, its reaction to this revolution is belated, but the company recognizes that it needs to improve its position in this space.

Within sites like Facebook, a lot of formerly dispersed online activities are united under a single virtual roof, making these sites very attractive for advertisers. That's because people share a lot of personal information about themselves on the sites, making the users easy to target with commercial pitches.

Of course, there are also question marks about advertising on social networks, primarily because their content is mostly unregulated and sometimes objectionable as it is generated by millions of individuals. In addition, social networking sites are under close watch by law enforcement agencies worldwide because sexual predators have used these sites to stalk and victimize others, including minors.

An earlier sign of Google's sense of urgency about the social networking market was its reported courting of Facebook when the latter was recently seeking a partner to invest in the company and earn a deal to provide advertising to it.

Microsoft eventually won, buying a 1.6 percent stake that values Facebook at an eye-popping $15 billion, although the social networking company reportedly will have revenue of just $150 million this year.

With about 300 employees, Facebook expects to have about 700 a year from now, its CEO and co-founder Mark Zuckerberg recently said. About 250,000 new users register every day at Facebook, which was founded in 2004.

In June, MySpace, owned by News Corp., had 114.1 million unique visitors worldwide, ranking first among social networking sites, followed by Facebook with 52.2 million, according to comScore. Hi5 ranked third with 28.2 million, while Friendster was fourth with 24.7 million. Orkut rounded out the top 5 with 24.1 million.

OpenSocial, which will launch officially Thursday evening, represents "the first release of technical details" for the forthcoming MySpace application development platform, Google and MySpace said on Thursday.