Microsoft Corp. has made an unsolicited offer to buy Yahoo Inc. for $44.6 billion in cash and stock, seeking to join forces against Google Inc. in what would be the biggest Internet deal since the Time Warner-America Online merger, Reuters reported today.

In its boldest-ever acquisition move, Microsoft said it offered $31 per share for Yahoo, or a 62 percent premium over the Internet media company’s closing stock price on the Nasdaq Stock Market Thursday.

Yahoo, whose shares jumped to $30.75 in pre-market trading, said it would evaluate the bid. Microsoft shares, which have a market capitalization of about $300 billion, fell 6 percent to $30.78.

Internet audience researcher comScore estimates Google’s share of the worldwide Web search market has reached 77 percent, while Yahoo is second with 16 percent and Microsoft is a distant third with 3.7 percent.

“Microsoft’s wanted to do things that could build up its online business dramatically. This is going to be a big bet for them,” said Brendan Barnicle, an analyst at Pacific Crest Securities. “But I also think it’s where they see the market going, so they really needed to get there. This is more than a shot across the bow at Google, because you put these two guys together who are basically two and three in search and it makes them far more relevant.”

The Microsoft-Yahoo deal would be the largest in the Internet market since the $182 billion purchase of Time Warner Inc by AOL in 2001, which was seen as the worst merger in recent corporate history, with clashing corporate cultures and many of the promised synergies never materializing, Reuters said.