Google on Wednesday sought to counter the growing power of Facebook, unveiling a strategy that it claimed could eventually spread the benefits of social networking to other unrelated websites.

Shares in Google rose above $700 for the first time as the search engine company revealed details of its plan, OpenSocial, which marks its response to the threat of social networking – a force that has emerged on the web this year.

Facebook has become Silicon Valley’s hottest company since the rise of Google after it “opened up” its site to other developers earlier this year.

That has let others add their own applications to its site, creating a race in the Valley to build new services for Facebook’s booming audience.

The risk that this could become a self-reinforcing spiral, as more applications attract a bigger audience and vice-versa, has led bigger rival MySpace to announce a similar strategy.

The technology that Google unveiled will let developers spread applications across any of the social networks that adopt it, removing the need to rewrite them for each one.

With more than 100m users between them, these networks should have a big enough audience to draw attention from developers, said Joe Kraus, the developer heading Google’s initiative. He described the move as the first step in a plan to break down barriers between social networking sites, eventually creating interfaces that would let users share their data and social connections without needing to belong to the same services as their friends.

Internet users would eventually be able to use their personal and social data on any internet service they wanted, he added, while also being able to communicate automatically with their network from anywhere on the web. However, while agreeing that this was the eventual vision behind OpenSocial, another member of the Google consortium warned that no agreements were yet in place to make this possible.

“What Facebook created was really revolutionary and kicked off an amazing paradigm shift,” said Ali Partovi, chief executive of iLike, another builder of applications for social networking sites. “We’re still in the very beginning of a long road.

“Whether Facebook continues to be not only the first mover but also the key beneficiary of this shift remains to be seen.”