Removing Internet browsing functions from Microsoft Corp.'s Windows 98 software could benefit consumers by saving computer memory and making the machine run faster, a Princeton University professor testified at the Microsoft antitrust trial yesterday. But in a live courtroom demonstration, the company showed that a program the professor devised to remove the browser from Windows does not necessarily prevent users from browsing.

Microsoft intended the demonstration, to which government lawyers strenuously objected, as a "gotcha" moment that would discredit the professor's testimony. But the judge conducting the trial showed little sign of being impressed, and refused a request by the company to present additional evidence about flaws in the removal program.

The government contends that Microsoft's Internet Explorer browser and its Windows operating system are two different products that should be distributed separately. By combining the two, the government alleges, Microsoft is using the market clout of Windows, which runs on 90 percent of the world's new personal computers, to illegally dominate the browser market.

Microsoft maintains that Internet Explorer and Windows are fully -- and legally -- integrated, and for programming reasons cannot be pried apart. The company also argues that including a browser in Windows makes it easier for computer users to get onto the Internet.

To make its argument that the Explorer and Windows are separate, the government called Princeton computer scientist Edward W. Felten to the witness stand. Felten had testified for the government earlier in the trial, and his one-day appearance in court yesterday largely was intended to rebut the subsequent testimony of several Microsoft executives, who asserted that the browser and operating system are inexorably intertwined and that Felten's browser-removal program slows down Windows.

Yesterday Felten said he conducted several tests comparing Windows computers with and without Internet Explorer. The results, he said, showed that the browser-less Windows machine ran somewhat faster and required significantly less computer memory.

In a potentially significant exchange, Judge Thomas Penfield Jackson asked the witness if a browser might make a computer more vulnerable to electronic viruses -- small programs that spread surreptitiously from machine to machine. The judge suggested that he could see a benefit from allowing consumers to get Windows without a browser.

Felten, who heads the Secure Internet Programming Laboratory at Princeton, replied in the affirmative. "You might well choose not to have a browser in order to prevent that means of spreading a virus."

Although Felten first presented his browser-removal program when he testified last year, he submitted a new version yesterday, one he said fixes flaws that Microsoft had criticized. But the new version didn't sit well with the company either, and it sought to torpedo it in a demonstration.

Placing a new Toshiba laptop computer on the witness stand, Microsoft attorney Steven L. Holley directed Felten to run his removal program. Holley then had him access a "Windows Update" screen, whereupon the lawyer instructed the witness to hold down the "Control" key and type "N." That opened up a browsing window, which Holley told Felten to use to access the Justice Department's Web site.

"Internet Explorer is running on this machine, is it not?" Holley asked Felten.

"It could be," responded Felten.

He said his program was a "proof of concept" that still could have bugs. And he argued that the presence of other software -- including other non-Microsoft browsers -- on the Toshiba machine could have affected the results.

"There are many ways in which Microsoft could go about delivering Windows 98 without Internet Explorer," Felten said. "The point of this is just to show that it is possible."

Jackson eventually cut off the demonstration, telling the attorney and witness they were in a "state of semantic non-reconciliation." Later, when Holley asked for permission to demonstrate on a machine with no other software, the judge curtly denied the request.