SAN JOSE, California — In a move aimed squarely at Microsoft, Sun Microsystems unveiled on Tuesday a suite of software for businesses that want to dump — or just can’t afford — the Windows operating system on their companies’ desktop computers.

The Sun Java Desktop system, which was formerly code-named Mad Hatter, runs on the open-source Linux operating system and includes a variety of programs that replace Microsoft’s Internet browser, productivity suite and other parts of the Windows package.

In Tuesday afternoon trading, Sun shares rose 16 cents, or more than 4 percent, to $4.02 on the Nasdaq stock market.

Sun officials say its system will cost as little as $50 per user per year and can be installed on any computer that can run Microsoft’s Office 2000. The software also is designed to interoperate with Windows-based programs such as Exchange and Microsoft Office.

“We’re talking about a radical savings — more than 75 percent over just the comparable upgrade cost for Microsoft,” said Larry Singer, Sun’s senior vice president of global market strategies.

Sun, a leading maker of high-end, Unix-based servers, has been struggling since the dot-com collapse to bolster sales as systems based on inexpensive x86 microprocessors and the Linux operating system have become more powerful and more viable.

The company has since embraced both x86 chips and Linux in an effort to become a leader in low-cost computing. The move toward desktops is another facet of that transformation.

But Tuesday’s announcement also echoes a theme heard throughout Sun’s nearly 20-year history: a desire to position itself as an alternative to Microsoft in desktop computing.

In the late 1980s, Sun’s 386i PC project flopped as the young company was then ill-prepared for the market. More recently, attempts to get support for its universal programming language Java in desktops have been hindered by Microsoft.

In fact, Sun’s $1 billion antitrust case over that matter is still pending in a Maryland federal court.

Sun’s latest attempt tries to leverage its Java brand, which is popular on a wide range of computing platforms from servers to cell phones but has contributed little directly to the company’s bottom line.

Singer said because of Java’s openness and integration with the new Sun desktop software, developers will have access to more components of the underlying software than they do with Microsoft’s proprietary offerings.

Singer said there’s another key difference between Sun Java Desktop and Microsoft Windows-based systems.

“Guess what? It wouldn’t have blown up … with the worms and the viruses” of recent weeks, he said.

Sun also announced a major upgrade to its StarOffice productivity suite. Singer said it would work better than previous versions with Microsoft’s competing Office suite.

Besides the desktop system, Sun also announced a suite of server software at its SunNetwork user conference in San Francisco. The software, formerly called Project Orion, has been officially named Java Enterprise System. It’s priced at $100 per employee per year.

“It’s kind of taking a page out of Microsoft’s books,” Singer said. “We are for the first time introducing a suite of products that have greater value as the sum of the parts than the parts themselves.”