San Francisco ? Microsoft Corp. is once again trying to team up with Yahoo Inc. to challenge Internet search and advertising leader Google Inc., although at this point the renewed talks haven’t escalated to another attempt to take over Yahoo.

The Redmond, Wash.-based software maker disclosed the revived discussions Sunday without providing any specifics about the nature of the deal being explored except to say it involved bolstering the companies’ position in the online search and advertising markets.

In a statement late Sunday, Yahoo said its board is exploring several “value maximizing” alternatives and “remain open to pursuing any transaction (that) is the best interest of our stockholders.”

Microsoft emphasized that it hasn’t resurrected a $47.5 billion takeover bid that its chief executive, Steve Ballmer, withdrew May 3 after Yahoo CEO Jerry Yang – acting on behalf of Yahoo’s board – demanded an additional $5.5 billion.

But Microsoft left open the possibility that it might dangle another buyout offer of Yahoo, depending on how the discussions progress between the two companies and their respective shareholders.