By Michal Lev-Ram

Yahoo chief executive Jerry Yang sent a letter to the Internet company’s shareholders late Wednesday in an effort to justify the company’s decision to reject Microsoft’s $44.6 billion buyout bid.

According to a document filed with the Securities and Exchange Commission, the letter was supposed to outline “the reasons the board believes that Microsoft’s (MSFT) proposal significantly undervalues Yahoo (YHOO) and is not in the best interests of Yahoo stockholders.” But Yang devoted most of his more than 1,000-word memo to pumping up Yahoo’s assets — including its brand name, its lead in display advertising and its “healthy” cash balance — and laying out the company’s goals.

“We have taken significant but disciplined steps to refocus our business on our objectives to become the starting point for the most consumers and the must buy for the most advertisers and enhance Yahoo’s long-term performance,” wrote Yang.

Earlier this week a number of Yahoo shareholders began speaking out in favor of selling to Microsoft or other potential bidders. But despite reports that Yahoo was negotiating with  AOL (owned by Time Warner (TWX), the parent company of Fortune and CNNMoney.com) and News Corp. (NWS), no other buyer has stepped forward. Still, Yang’s shareholder letter implied he still thinks keeping Yahoo independent is a realistic option.

“Today, Yahoo is a faster-moving, better-organized, more nimble company than it was just a few months ago,” Yang wrote. “The fact is that we are well on our way to transforming the experiences of Yahoo’s users, advertisers, publishers and developers — an important shift that is at the heart of our plan to create stockholder value.”