SAN JOSE, Calif. – If not for Google’s first three flops at social networking, the search giant might never have come up with a viable challenge to Facebook and Twitter.

Google’s fourth and most ambitious attempt at social networking has set Silicon Valley abuzz, with membership soaring past 10 million people in just three weeks. Vic Gundotra and Bradley Horowitz, the two executives in charge of Google+, said in an extended interview that they closely studied Google’s previous failures with Orkut, Wave and Buzz to find a better approach. They also found a close-knit team of engineers and designers willing to take a risk.

Google+ ranks as one of the most important product launches in the company’s history as it tries to catch up with the booming success of 750 million member Facebook and other social sites, and the threat they represent to Google’s advertising business. Google+ is the centerpiece of a companywide master plan to reboot Google for a modern Web that is increasingly about connecting with people as well as information.

Although the numbers for Google+ are impressive, Gundotra and Horowitz said it’s far too soon to declare Google+ a winner. “We’re Google. We can get anybody to kick the tires of a product,” said Gundotra, the Internet giant’s top social networking executive. “It doesn’t mean it’s going to be successful.”

Sitting in Building 2000 on the Googleplex, where they assembled the team in June 2010 to build Google+, the two executives talked about the leap of faith they made, and the team of engineers and designers that built the network.

“We’ve got some great characters here,” Gundotra said. “Good people who are gelling together as a team. I think that’s a part of the story that has never been told. People don’t get how magical this team is. How we came together in the course of the past year to become friends.

“We’re a heated team, a passionate team, lots of good fights, but it’s a team that is pretty amazing.”

Experts agree it’s too early to call the social network a hit, even though its popularity helped push Google stock up 13 percent last week. Indeed, Facebook added 250 million members in the year Google+ was being designed. “Until it really starts to go mainstream, and I see my cousin in Florida decide to get on it, I just don’t think we can say it’s a success. We’ve got a ways to go,” said Michael Fauscette, an analyst with IDC.

But the stakes have rarely been higher for Google. Social networking failures like Wave and Buzz are “the glaring failure in their history – the thing they had failed to do – which was to bring people into their products,” said Steven Levy, who followed the Google+ team, code named “Emerald Sea,” as he reported his new book, “In the Plex.” “In the heads of all the people at Google, right up to the very top, it became clear that this was something that was essential to Google’s very survival.”

Gundotra, a former Microsoft executive who had already become one of Google’s most public faces because of his fluid speaking style at product launches, was tabbed by co-founders Larry Page and Sergey Brin and former CEO Eric Schmidt to take the reins of the next social effort. What struck Gundotra 13 months ago was the makeup of the Google team.

“These were all the nutty people,” Gundotra said. “Why in the world would you work on yet another social product at Google? You had to be pretty nutty. You had to be entrepreneurial. You had to be willing to take risks. There was very little reason to have faith that this effort would be more successful than the earlier ones.”

“This wasn’t a project that was a surefire winner, or a nice place to coast,” Horowitz agreed. “This was a project that required passion just to show up every day, and a willingness to sort of tilt at windmills – a startup-level passion.”

The team included Andy Hertzfeld, a 57-year-old engineer who was on the team that designed the Macintosh computer at Apple in the early 1980s. Hertzfeld built some of the initial software for Circles, the Google+ feature where members get to connect with others. A little green bubble floats to the top of the page when a user drops a connection into one of their Circles.

“Andy is a tremendous talent,” Horowitz said. “I think his spirit, his whimsy, his approach shines through.”

While the Google team recently added another 1980s Apple veteran, Bill Atkinson, Hertzfeld has said stories that Google built the network by tapping Apple’s design genius are off-target, and that the contributions of “awesome young” team members like Shaun Modi, Jonathan Terleski and Joseph Smarr were huge.

The team huddled together on a single floor of Building 2000, where they could have discussions and debates and trouble-shoot problems on the way to the restroom or to have lunch, without having to schedule a meeting.

They created team traditions like “Formal Fridays,” in which everyone had to dress with increasing formality each week until launch. “What started out as blazers turned into tuxedos for some people. It was fun to sort of create that cultural tradition,” Horowitz said. “It was also uncomfortable in the sense that the last thing engineers want to do is dress up. So the longer we delayed launch, the worse it was going to get. So it created a good incentive.”

Gundotra and Horowitz said Google’s many failures in social networking turned into an advantage. The team started by trying to figure out what they learned from the failures of Buzz, Orkut and Wave. Then, they listened to users talk about what they liked and didn’t like about current social services.

Horowitz believes the dizzying array of social products from Facebook to Twitter to Flickr to LinkedIn have befuddled the average user. “What we found was that sharing was fundamentally broken on the Net. It’s not that there weren’t a million ways to share; it’s that there were a million ways to share. They weren’t coherent.”

Google internal data shows that users are two to three times more likely to share content within one of their Circles than to make a general post. But Google+ is far from a finished product. Among the more glaring absences is the lack of ads. Nor does it have the massive list of games and other apps built by independent developers and outside companies like Zynga that run on the Facebook platform. There has been criticism that Google+ is too male-centric, although Gundotra and Horowitz dispute that, saying women in particular are doing more sharing in private circles rather than public posts.

Google won’t disclose current numbers, although estimates of 10 million users “sound very stale to me,” said Horowitz. Google is struggling to accommodate businesses, as well as an influx of celebrities like actors Alyssa Milano and William Shatner and rapper 50 Cent.

“We did not anticipate this much this soon, in terms of traffic and passion of users,” Horowitz said. “We thought we had the due course of time to get it right before the world came to our doorstep. The world is at our door, and they want it, and they want it now.”

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