BALTIMORE (Reuters) - A federal judge hearing Sun Microsystems Inc.'s SUNW.O antitrust suit against Microsoft Corp. MSFT.O , said on Tuesday that forcing Microsoft to carry Sun's Java software in the Windows operating system could be an "attractive" remedy.

U.S. District Judge J. Frederick Motz had tough questions for both companies during opening arguments, but was sympathetic to letting Sun's Java compete without "the distortions of the market wrought by the violations Microsoft has done."

"It is so much nicer than having ... economists try to figure out what would have been," the judge said.

Microsoft dropped Java, a computer language designed to run on various operating systems, when it introduced Windows XP last year. It later reversed itself and said it would start including Java in a Windows XP update, but only until 2004.

Microsoft attorney David Tulchin pointed out to Motz that a judge in the long-running government antitrust case against Microsoft had recently rejected a Java must-carry demand by nine states seeking stiffer sanctions in that case.

Motz said he was not bound by Colleen Kollar-Kotelly's Nov. 1 settlement order.

"I was surprised at the vehemence with which Judge Kollar-Kotelly rejected (the must-carry proposal)," he said.

Motz is also overseeing other antitrust lawsuits filed against Microsoft. AOL Time Warner AOL.N unit Netscape Communications, Be Inc. and Burst.com BRST.OB have filed legal action, in addition to consumer class-action suits.

Sun filed its suit in March after a federal appeals court, in June of 2001, upheld a lower court ruling that Microsoft had broken U.S. antitrust laws and illegally maintained its monopoly over personal computer operating systems.

The appellate judges said Microsoft had promoted a "polluted" version of Java to deceive Java developers and protect its Windows operating system.

Motz asked Microsoft why he shouldn't grant Sun's must-carry request on Java, saying it was an "attractive" remedy.

Tulchin, for Microsoft, said Sun wanted a "free ride" on Windows because it was unwilling to do the hard work of getting Java distributed to computer users.

"The antitrust laws were not promulgated so that one competitor could take a free ride on the back of another competitor," Tulchin said.

Motz asked Sun why it needed Java distribution via Windows if it was a better product than Microsoft's .Net services.

Sun's attorney, Rusty Day, told the judge that Microsoft should be forced to distribute Java as part of Windows, because Microsoft plans to use .Net to wipe out Java.

Day, citing previous court rulings that concluded Microsoft had taken illegal steps to hobble Java, asked: "Will this court call foul" or "will it allow Microsoft to exploit all the disadvantages that it illegally inflicted on its competitor?"

The hearing was due to continue with testimony from witnesses called by Sun and Microsoft.