The effort is particularly important for Facebook, which once represented the seemingly boundless promise of the Web 2.0 boom. It desperately wants to make certain the other Web companies do not supplant it and become the most popular hub for online socializing.

Image The screen you would see when logging into Citysearch, a Facebook partner, with your Facebook Connect credentials.

Facebook, with 120 million members worldwide, has also been under extra pressure to get its revenue to match its media hype and membership growth. Responding to reports that Facebook was looking for more capital after raising $235 million last year, Ms. Sandberg said she would not rule that out. “There is a lot of interest in investing in us and we are always open to the right financing at the right price,” she said.

The most immediate challenge confronting Facebook is to create an enduring stream of advertising revenue.

A survey last week from the research firm IDC suggested that social networks were a miserable place for advertisers: just 57 percent of all users of social networks clicked on an ad in the last year, and only 11 percent of those clicks led to a purchase, IDC said. And it turns out that marketers are not so interested in advertising on pages filled with personal trivia and relationship updates.

“What in heaven’s name made you think you could monetize the real estate in which somebody is breaking up with their girlfriend?” Ted McConnell, a general manager at Procter & Gamble, asked last month at an industry conference.

This is where Facebook Connect could help. No money changes hands between Facebook and the sites using Connect, and executives are wary of discussing how it could bring in revenue. But there are some obvious possibilities.