A federal judge in Baltimore ordered Microsoft Corp. yesterday to package with its Windows operating system a computer programming language made by Sun Microsystems Inc.

The ruling stems from Sun's allegations that Microsoft "committed anticompetitive acts" to thwart the distribution of Java, a computer language made by Sun that also runs applications on top of an existing operating system. Sun also alleged that Microsoft is taking advantage of past antitrust violations to gain a monopoly in a chunk of the personal computer market.

To remedy the situation, Sun asked Chief U.S. District Judge J. Frederick Motz in a three-day hearing this month to instruct Microsoft to set up Java to run on any products that run Microsoft's .Net platform, an alternative to Java. Those products include Microsoft's Windows operating system, found on more than 95 percent of all personal computers. The legal action here was part of Sun's $1 billion antitrust lawsuit against Microsoft. Sun had said that if it waited until the lawsuit was settled, it would be too far behind to compete.

In his 42-page opinion filed yesterday afternoon, Motz wrote that, "unless the injunction is granted, there is a substantial risk that the market for general purpose, Internet-enabled distributed computing platforms will 'tip' irretrievably in favor of .Net and drive Java into near-extinction."

Yesterday's injunction comes on the heels of a settlement between Microsoft and the federal and state governments in an antitrust case in which Microsoft was found to have violated federal laws by monopolizing the market for operating systems that run personal computers. The Justice Department and nine states, including Maryland, had agreed to a proposed settlement with the software giant, and U.S. District Judge Colleen Kollar-Kotelly accepted the settlement with few changes -- a move that was widely considered a huge victory for Microsoft.

Ken Smiley, senior industry analyst for Giga Information Group in Cambridge, Mass., said that yesterday's ruling by Motz was not a major loss for Microsoft, either.

Sun's Java and Microsoft's .Net are two extremely different products, Smiley said. Forcing Microsoft to package Java with Windows is like making Ford ship a car with a Chevy engine, though to a lesser extreme, he said. "The short term is, what does that mean logistically for Microsoft to have to put something from Sun in the box with Microsoft software?" Smiley said.

Microsoft can make Java so difficult to use that customers will chose to use .Net instead, he said.

"This decision is a huge victory for consumers who will have the best, latest Java technology on their PCs," said Mike Morris, a Sun vice president, "and it is a victory for software developers who will write applications to run on those PCs."

Microsoft spokesman Jim Desler said the company still needs to review the details of the decision, but initially plans to appeal.

"We're disappointed with today's ruling," said Desler, adding that it was "premature at this point," to comment on when the latest version of Java will be included in the Windows system.

Smiley also said that Microsoft is likely to appeal the decision, asking the appellate court to stay the lower court's decision during the appeal process.

But Motz stated in his opinion that if the injunction was not granted, the potential harm to Sun would be great, while the potential harm to Microsoft if the injunction is granted would be small.

"If, as Microsoft asserts, the granting of preliminary relief is extraordinary, the short answer is that extraordinary circumstances require extraordinary remedies," Motz wrote.

The opinion was released after the stock market closed yesterday. Shares of Sun fell 5 cents to $2.96 in regular trading, then rose above $3.25 after hours. Microsoft rose 96 cents to $54 in the regular session, then eased about 10 cents after hours.

Sun and Microsoft officials will consult over the holidays and then meet with Motz in January to work out how to implement the order, said Lee Patch, Sun's vice president for strategic litigation.

The Associated Press contributed to this article.