SAN FRANCISCO – In a battle to woo back Web surfers who are spending more time on social networking sites, Internet portal Yahoo has clinched a deal with Twitter to share content across both properties.

Yahoo reached a similar agreement with Facebook in December, expanding the partnership to make it easier for users to share Facebook status updates and other information on Yahoo or share Yahoo sports scores or Flickr photos on Facebook.

Twitter offers millions of messages posted every minute. ”The information in one single tweet can travel light years farther with this Yahoo integration,” Twitter co-founder Biz Stone said in a statement. ”Tweets in more places brings relevance where and when you need it most.”

The move reflects Yahoo’s deep desire to tap into the increasingly social nature of the Web, a trend propelled by Facebook and Twitter, which have become major forces in driving and directing traffic. Yahoo missed its golden opportunity to cash in on the rise of social networking when Facebook rebuffed its $1 billion-plus takeover offer. Its current strategy has its critics.

The partnerships with Twitter and Facebook will take effect later this year. The partnership with Twitter will allow users to take material from both sites without having to leave either one, said Jim Stoneham, vice president of communities for Yahoo.

Specifically, users will be able to access their Twitter feed on Yahoo’s sites, update their Twitter status and share content from Yahoo in their Twitter feed, while Yahoo search and media properties will include Twitter updates. Twitter will start showing up in Yahoo search results right away.

”We are focusing on making Yahoo where you can stay in touch with people and information in one place,” he said. ”We hear consistently from a good chunk of our user base that the Web is too cluttered and confusing.”

So what’s happening at Twitter? Twitter is inking all kinds of non-exclusive deals. It has search deals with Microsoft and Google. It has deals with AOL and MySpace. The corporate philosophy: The more places to tweet, the better.

Transforming popularity into profitability may be a big bonus. The search deals that were announced in October reportedly will generate about $25 million for Twitter.