But Google is painting a starkly different picture, asserting that Microsoft will be able to stifle innovation and leverage its dominating Windows operating system to set up personal computers so consumers are automatically steered to online services, such as e-mail and instant messaging, controlled by the world's largest software maker.
In a move that illustrates just how badly Google wants to torpedo the deal, Google Chief Executive Officer Eric Schmidt called Yahoo CEO Jerry Yang Friday to offer his help in repelling Microsoft, according to a report Sunday on The Wall Street Journal's Web site, which cited anonymous people familiar with the matter.
The assistance didn't include a counterbid, but may have included supporting other potential suitors, or a revenue guarantee in exchange for an ad partnership with Yahoo, the people said, according the newspaper.
AT&T, Time Warner and News Corp. aren't planning to enter the bidding, the Journal said, citing the people familiar.
To help make its point, Google pointed to the way Microsoft previously used Windows to help extend the reach of its Web browser and other applications -- a strategy that triggered a U.S. Justice Department lawsuit alleging the software maker illegally used its operating system to stifle competition. The dispute ended with a 2002 settlement that required Microsoft to abandon some of its past practices.
"Could Microsoft now attempt to exert the same sort of inappropriate and illegal influence over the Internet that it did with the PC?" Drummond wrote.
Brad Smith, Microsoft's general counsel, said preventing Microsoft from buying Yahoo would undermine competition by allowing Google to become even more dominant than it already is on the Internet
"Microsoft is committed to openness, innovation, and the protection of privacy on the Internet," Smith said. "We believe that the combination of Microsoft and Yahoo will advance these goals."
If they get together, Microsoft and Yahoo would have about 16 percent of the worldwide Internet search market -- still far behind Google's 62 percent share, according to comScore Media Metrix. But Microsoft and Yahoo already are far bigger in than Google in e-mail and instant messaging, and conceivably would be in a better position to squash rival services if they combined.
Illustrating the enormous stakes involved in a deal that could reshape the technology and media industries, Google and Microsoft are already debating the pros and cons before Yahoo has responded to the offer.
In its Web site posting, Yahoo has said its review of the proposal "will include evaluating all of the company's strategic alternatives, including maintaining Yahoo as an independent company."
Most analysts believe Yahoo will have little choice but to sell to Microsoft, with its stock price near a four-year low at the time of the bid and its profits falling since late 2006. When it was first announced, Microsoft's offer was 62 percent above Yahoo's market value -- a premium analysts doubt any other suitor will be able to top.
If Yahoo accepts, antitrust regulators in both the United States and Europe are expected to begin an exhaustive review that some experts think could last a year. Microsoft believes it could get the necessary approvals to take over Yahoo late this year.
"It's a very defensive display of fear against what it appears to be a new empire, which is Google," Aleksandra Bosnjak, an analyst at StrategyEye Digital Media, told "Worldwide Exchange."
"Short-term I don't think there will be any implications for Google. Long-term, however, Microsoft is likely to put some interesting things against Google," Bosnjak said.
If nothing else, Google's comments probably will try to raise enough alarms about the Microsoft-Yahoo deal to delay its approval for as long as possible. By doing so, Google would have more time to draw up plans to counteract the combination.
Google also is borrowing a page from Microsoft's book by urging antitrust regulators to take a hard look at the proposed marriage between its two rivals.
Just days after Google struck a $3.1 billion deal to buy online ad service DoubleClick Inc. last year, Microsoft began lobbying regulators to block the transaction. U.S. regulators blessed Google's DoubleClick acquisition late last year after an eight-month review, but the antitrust inquiry in Europe remains open.
--The Associated Press contributed to this report.
--CNBC.com has business relationships with both Yahoo and Microsoft.