Yet another round of courtroom battles opened yesterday for Microsoft Corp., as the software giant continues to face repercussions from its violations of U.S. antitrust laws.

Sun Microsystems Inc., one of Microsoft's most bitter rivals, asked a federal judge in Baltimore to temporarily force Microsoft to include Sun's Java software code in all copies of Microsoft's dominant Windows operating system. Sun is suing Microsoft for antitrust damages in a case that could take years, and Sun wants the judge to require the Java distribution until the case is resolved.

Although Microsoft won a major victory a month ago when a federal judge in Washington approved a settlement between the company and the Justice Department, the company must now shift gears to fight antitrust lawsuits filed by corporate competitors and consumers who claim they were damaged by Microsoft's illegal conduct.

Those suits, combined with a pending decision by European regulators on similar antitrust issues, are slowing Microsoft's efforts to put its legal woes behind it and turn a new chapter in its corporate history. Two states, Massachusetts and West Virginia, also are appealing the approval of the Justice Department settlement.

In addition to the Sun lawsuit, Microsoft is being sued by AOL Time Warner Inc. and Be Inc., a small operating system manufacturer. All are hoping that a federal appeals court ruling last year -- which affirmed that Microsoft illegally protected its operating system monopoly -- will lead to significant monetary awards.

At least in their early stages, the corporate suits are being heard by U.S. District Judge J. Frederick Motz, who already has rejected a proposed settlement in one set of class-action cases. A larger class-action case is scheduled for trial in California early next year.

Sun's is the first corporate suit to reach the courtroom, with Motz opening a three-day hearing to consider the company's request for the temporary order forcing the distribution of Java. Java code enables certain Internet-based applications, such as charts that update with new data automatically, to operate regardless of which operating system is in use.

More broadly, Java is a set of programming tools that allows software developers to write applications for any computing systems, including those that run servers, that power handheld organizers or operate cell phones that do more than make phone calls.

In Sun's view, Microsoft is preparing an assault to dominate the brains of these devices, just as it does personal computers. Microsoft's new .Net collection of applications, which enables a variety of Internet-based interactions but is linked closely with Windows, is designed to compete with Java.

But Sun charges that once .Net is bundled with Windows, which will put it on roughly 90 percent of the world's personal computers, software developers will naturally choose it over Java.

Harkening back to the federal government's case against Microsoft, Sun attorney Lloyd R. Day Jr. said that Microsoft originally sought to neutralize Java by introducing its own version that was not compatible with Java and by deceiving developers about its capabilities.

Microsoft's actions to undermine Netscape, the first Internet browser to carry Java, cut off Sun's distribution system, Day said. And this bought Microsoft time to develop a competitive product, he argued.

"It's one thing to compete on the merits and earn the gold medal," Day said. "It's another to take out a competitor's knee."

Microsoft attorney David B. Tulchin countered that Sun was seeking to take "a free ride on the back of Microsoft" by demanding Java distribution.

He noted that a similar proposal by state attorneys general was rejected by the judge who approved the settlement agreement with the Justice Department. And he said that Sun is free to cut deals with computer manufacturers to have them pre-install Java on new computers.

Users of computers that do not have Java can download it from the Internet.

As for other devices, Tulchin argued that since .Net is not yet deployed with Windows, Java rules the non-personal-computing landscape and thus cannot demonstrate immediate harm that would occur if Java is not distributed via the operating system.

But at one point, the judge wondered aloud whether, since requiring Java on Windows would not detract from .Net, Sun's request was a "wonderfully elegant" solution. Motz noted the "Netscape experience," in which Microsoft quickly dominated the market for Internet browsers after acting to choke off Netscape's distribution through deals that were found to be illegal.

Antitrust experts, however, said that Sun's request is a long shot.

"It's exceedingly rare for judges to order affirmative conduct pending these trials," said Hillard Sterling, a Chicago lawyer specializing in technology antitrust cases. "It's doubtful that Sun can show that absent the injunction, it would suffer injuries that couldn't be addressed later."