Microsoft trial-watchers long believed that the weakest part of the Justice Dept.'s case was its allegation that the software giant illegally bundled its Internet browser into the Windows operating system. But the government scored big points earlier in the trial when Edward W. Felten, one of the government's expert witnesses, testified that he had developed software that could remove Internet browser functionality from Windows 98 without degrading the operating system.

On Jan. 27, debate moved back to Microsoft's turf with the submission of written testimony by Senior Vice-President James Allchin. He testified that his analysis of Felten's test uncovered "serious errors." Allchin noted that Felten never actually removed Internet Explorer from Windows 98 but only hid the browsing feature from consumers. He noted that users could still find it if they knew how to. Most important, he said, Felten's software "breaks useful features" of Windows 98, degrades the performance of the operating system, and prevents customers from using some applications, including Lotus Notes.

Allchin's testimony goes to the very heart of Microsoft's defense. The government argues that the company illegally bolted together two separate software products -- Windows and the browser -- as a way to harm a rival browser developed by Netscape Communications Corp. Justice claims that computer makers and consumers would be less likely buy the Netscape product if Microsoft's browser already is included in its operating system. But Microsoft contends that Internet Explorer is an integral part of the operating system and that such integration makes computing easier for end users.

Allchin wrote that the same software code that provides Web browsing functionality also provides support for developers and access to information stored in locations other than the Internet. If IE were removed, the operating system would not work.

FEWER HASSLES. In his written testimony, Allchin argues that in the fast-paced high-tech world, it doesn't make sense to establish "artificial boundaries" between software components. For years, he wrote, the trend in the computer industry has been to integrate increasing numbers of features. Consumers get better value for their money and fewer hassles. Developers like it this way because much of the basic software code they would ordinarily have to write themselves is already included in the operating system. By tightly integrating the browser, he notes, there are additional benefits "that simply can't be achieved through the use of add-on products from third parties."

On Jan. 28, Justice and Microsoft will argue over a motion to release E-mail from a Microsoft official regarding its testing of Felten's software. Microsoft argues that it's privileged. Sources close to the case say that E-mail will show that Microsoft's own tests prove that it is possible to remove browser code from the operating system without hurting Windows. In the afternoon, Allchin will use video displays to show how he tested Felten's program.

Justice is scheduled to cross-examine Allchin on Feb. 1.

By Susan Garland in Washington