Google Inc transformed the Internet by cataloging the Web's countless pages. Now it wants to keep better track of the Web's multitude of users.

The Mountain View, California-based company said Tuesday it would begin encouraging websites and mobile apps to accept log-in credentials via Google+, its social network.

The integration with third-party sites and apps, which Google hopes will help it track users as they surf across the Internet, represents the search powerhouse's latest effort to establish a foothold in the all-important social Web arena, and beat back competition from Facebook Inc, the sector leader.

Sites that have so far agreed to accept Google's social sign-in include The Guardian and USA Today's websites, as well as Fancy, the shopping site, and Fitbit, the personal fitness-tracking service and app, Google said in a blog post Tuesday.

Since 2008, Facebook has been able to gather massive troves of information about its users' activities even if they are not on Facebook because many popular apps, such as Spotify's music streaming service, allow users to log in with their Facebook identity, which results in data funneled back to the social network.

In response to Facebook's rise, Google has made its social Web efforts a top priority in recent years. But results have been mixed under the leadership of Chief Executive Larry Page and Vic Gundotra, the influential senior vice president spearheading Google's social networking efforts.

Launched in 2011, Google+ still lags far behind Facebook: it had 100 million monthly active users in December, according to comScore, compared to well over 1 billion for Facebook. But Google officials have downplayed the lukewarm public reception, saying they view Google+ more as an invisible data "backbone" that tracks individual users across its various properties, and less as a consumer Internet destination.

Over the past year the company has made changes to the log-in process at its YouTube subsidiary, for instance, in order to nudge the video site's 800 million users to sign in and leave comments with their Google+ accounts rather than anonymous handles.