The state attorneys general still pursuing the antitrust case against Microsoft Corp. have asked a federal judge to force the company to show them the inner workings of the Windows operating system.

In a bid to pry open one of the world's most valuable pieces of intellectual property, the states argued they need to see the Windows source code in order to verify Microsoft's claim that it is not technically feasible for the company to offer a stripped-down version of the operating system.

"Microsoft cannot base its defense on the design of its source code and simultaneously deny the litigating states the opportunity to test those arguments by interrogating the code," the states said in their filing.

The motion was filed with U.S. District Judge Colleen Kollar-Kotelly on Tuesday and made available Wednesday.

As part of their proposed sanctions against Microsoft, the states have told Kollar-Kotelly that she should order the company to offer a stripped-down version of Windows, without any additional features such as its Internet Explorer browser.

In demanding to see the Windows source code, the states said the legal questions in the case "cannot be fairly resolved when the very subject matter in dispute is hidden from all but Microsoft's own employees."

Andrew Gavil, a professor of antitrust law at Howard University, said Microsoft could have a hard time refuting that argument.

"This is the equivalent of demanding of Coke that they turn over the formula," Gavil said. "This is exactly what Microsoft wanted to avoid."

In Tuesday's motion, the states also asked the judge to appoint a technical expert to help provide "impartial opinions on the complex, highly technical issues raised by the parties."

Microsoft has rejected both requests when approached directly by the states.

Microsoft spokesman Jim Desler said the company had proved during the trial that it is impossible to remove software features from Windows without damaging the operating system.

"They're trying to relitigate issues that they did not prevail upon in the court of appeals," Desler said. "And, in doing so, they're trying to complicate this case unnecessarily."

Desler said state attorneys general are working "hand-in-hand" with Microsoft competitors, who "will stop at nothing to get access to our intellectual property."

Microsoft reached a deal with Justice in November to settle the long-running case. Nine of the 18 states in the lawsuit agreed to sign on to the deal, but nine others are pressing ahead and asking the judge to impose stricter sanctions.

During the trial, the government accused Microsoft of using its Windows monopoly to snuff out competitors who make add-on "middleware" products, such as Netscape Communications Corp.'s Navigator browser.

In a landmark ruling on the case in June, a federal appeals court dismissed parts of the government's case, but upheld a lower court's conclusion that Microsoft had used illegal tactics to maintain the Windows monopoly.

Among the illegal tactics cited by the court was the "commingling" of Windows source code with add-on middleware.

The dissenting states -- including California, Massachusetts, and Connecticut -- say the availability of a stripped-down browser, without all the would help restore competition to the software business.