Apple launched a faster and feature-laden version of Safari 4 into public beta Tuesday, joining rivals Microsoft and Google in bidding for browser market share.

Apple called the new Safari browser “the world’s fastest,” saying that its underlying “Nitro engine” runs JavaScript 4.2 times faster than Safari 3.

In September, No. 1 Internet search company Google entered the Internet browser market with its Chrome software for Windows. A version for Apple’s Macintosh has yet to be released. Microsoft, which had 67.6 percent of the market as of January according to Net Applications, is scheduled to roll out Internet Explorer 8, a new version of its browser, later this year. Safari ranks third with 8.3 percent of the market, behind Mozilla’s open-source Firefox, with 21.5 percent.

Among the new features on Safari 4 are: Top Sites, which lets users visually preview their favorite web pages; Cover Flow, which lets users flip through web histories or bookmarks as they would flip through album covers on an iPod, and Full History Search, a tool for searching titles, web addresses and text of recently viewed pages.

Browsers have become increasingly important as more computer applications migrate off the users machine and onto the “cloud,” server farms hosted by companies like Google, Apple and Microsoft.

Safari 4 is based on the open-source WebKit code developed by Apple. Google used WebKit to develop Chrome and its mobile Android browser as Palm did in developing the browser for its new webOS operating system.

The Safari 4 beta is available for a free download to Mac OSX and Windows users at ww.apple.com/safari.