MENLO PARK Although Facebook has a powerful presence on personal computers, the cellphone has been its Achilles' heel. With its users flocking to mobile phones by the millions and many of its newest users never accessing the services on computers at all the company has struggled to catch up to them.
On Thursday, Facebook unveiled its most ambitious effort to crack the challenge: a package of mobile software called Facebook Home designed to draw more users and nudge them to be more active on the social network.
The new suite of applications effectively turns the Facebook news feed into the screen saver of a smartphone, updating it constantly and seamlessly with Facebook posts and messages.
In so doing, Facebook has cleverly, perhaps also dangerously, exploited technology owned by one of its leading rivals, Google. Facebook Home works on Google's Android operating system, which has become the most popular underlying software for smartphones in the world.
The Facebook news feed appears as the phone is turned on. Pictures take up most of the space, with each news feed entry scrolling by like a slide show. Messages and notifications pop up on the home page. To "like" something requires no more than two taps. Facebook apps are within easy reach.
"Today, our phones are designed around apps, not people," said Mark Zuckerberg, Facebook's chief executive, said at a news conference at the company's headquarters. "We want to flip that around."
Facebook Home will be available for download from Google's app store, Play, next Friday for four popular, moderately priced phones that use Android and are made by HTC and Samsung. A new model called the HTC First, will be sold by AT&T for $100 with the software loaded.
For the time being, Facebook will not show ads on the phone's home screen, which Facebook is calling "cover feed." Since advertising revenue is crucial to the company's finances, however, it will almost certainly display ads there in the future.
Facebook Home is also clearly designed to get Facebook users to return to their news feeds even more frequently than they do now. Every time they glance at their phone they will, in essence, be looking at their Facebook page.
"It's going to convert idle moments to Facebook moments," said Chris Silva, a mobile industry analyst with the Altimeter Group. "I'm 'liking' things, I'm messaging people, and when ads roll out, I'm interacting with them and letting Facebook monetize me as a user."
Krishna Subramanian, the chief marketing officer at Velti, a San Francisco-based company that buys targeted advertisements online on behalf of brands, pointed out that even without showing ads on the mobile cover feed, Facebook Home could prove to be a lucrative tool.
By nudging its users to do more on the social network, he said, the company will inevitably get "an explosion of mobile data that can be tied back into desktop advertising" to Facebook users.
A majority of Facebook's 1 billion-plus users log in on their cellphones. Most Americans now have an Internet-enabled phone, and smartphone penetration is growing especially fast in emerging market countries, where Facebook has substantial blocs of its users.
Although HTC is rolling out the first new phone with Facebook Home installed, and AT&T has agreed to sell it, other phone-makers and carriers may be reluctant to load the software. Jan Dawson, a telecom analyst at Ovum, said Apple's iPhone and many Android phones already do a good job of integrating the Facebook application into their phones.
Thursday's announcement signaled that Facebook had stopped short of building an operating system. Instead, it had simply altered its rival Google's technology.
The Android platform, Zuckerberg said, was built to be open to new integrations. Asked whether he feared that Google executives would change their mind about Facebook using it to advance its mobile aims, Zuckerberg turned somewhat testy.
"Anything can change in the future," he said. "We think Google takes its commitment to openness very seriously."
Google, for its part, was notably genteel. "This latest collaboration demonstrates the openness and flexibility that has made Android so popular," the company said in an emailed statement.