The U.S. meets Microsoft Corp. in a federal courtroom on Oct. 19, and the outcome of this landmark antitrust case could well determine the future of how we work, play, and shop well into the 21st century. No company has influenced the New Economy as much as Microsoft. So whether it's ultimately left alone or reined in will have repercussions in every household and office in America.

The stakes for both sides are huge. The case could settle the contentious debate over what the federal government's antitrust role should be in the Digital Age, where unfettered creativity has made the nation's computer industry the most admired in the world. The Justice Dept. and 20 state attorneys general contend that the geniuses of Microsoft went way too far, eventually using the company's market power to stifle other innovators of potentially better products. The endgame will determine whether the government -- which has suffered embarrassing defeats in the past in big antitrust cases -- will have any clout left to take on other cases involving dominant corporations.

Meanwhile, Microsoft's entire business strategy is on the line. If it wins, it will have clear sailing to do just about anything it wants in the software industry -- and perhaps in others as well. If it loses, the dominance of its core Windows operating system could weaken if not crumble, and that could set off a domino effect in related products. Even if a court finds only that Microsoft is a monopolist, rejecting all of the government's other charges, that alone could open the floodgates for private corporate litigants, who will be spared the arduous task of determining Microsoft's market power.

A WHO'S WHO. The trial is expected to last six to eight weeks. And while the testimony may often degenerate into techno-speak and antitrust jargon, there'll be plenty of compelling moments. A Who's Who of the computer world -- Netscape, Apple, Sun Microsystems, Intel, and Intuit -- will parade through the courtroom to be examined and cross-examined by two veteran litigators, David Boies for Justice and John Warden for Microsoft. Tantalizing E-mail and other evidence describing some of the industry's best-kept secrets will open a window into the wheeling and dealing of Silicon Valley.

The first witness will be Netscape President James Barksdale, who will describe, among other things, a key meeting with Microsoft that's the centerpiece of Justice's case. At the heart of that case is the government's contention that by 1995, Microsoft perceived two new threats to its Windows operating system: an Internet browser developed by Netscape and the Java software programming language created by Sun Microsystems Inc. Together, the two developments could have eroded Windows by enabling software developers to write applications that could run on any system on the Internet. If that trend caught on, no particular operating system would be more important -- or much better -- than any other.

The government claims that Microsoft tried to persuade Netscape to "divide the market" -- and sell its browser only for use on non-Windows systems. Once Netscape rejected that proposal, the government claims, Microsoft set out to kill Netscape -- or "to cut off Netscape's air supply," in the words of one executive. Microsoft integrated its own browser into its operating system, discouraging PC makers from incorporating Netscape's product into their machines. It also licensed Java, created a Windows-only version, and pressured software writers to use it. And it tried to induce Apple and Intel to limit their support for Netscape's browser and Java, according to the government.

NEFARIOUS INTENT? Microsoft argues that the purpose of this smoking-gun meeting with Netscape was to forge a "strategic partnership," and that such meetings between competitors are common practice in Silicon Valley, where companies try to ensure that their technologies work well together. At the trial, Microsoft is likely to offer evidence that friendly meetings between the two companies took place well after the so-called collusion discussion.

The software giant also will argue that it integrated its browser into the Windows operating system because that makes computing easier -- not because of any nefarious intent. And it will argue that seemingly damaging E-mail was informal banter and was taken out of context. If Netscape is losing market share, it will further argue, that's because the company's browser isn't as good as Microsoft's.

Neither side is an odds-on favorite to win. This is not a contest between David and Goliath, but one between equally matched Samson and Goliath. Still, Justice may have the edge going in. U.S. District Judge Thomas Penfield Jackson has been skeptical of Microsoft's arguments so far. But a conservative appeals court has been considerably more sympathetic to Microsoft, ruling in a related case that judges should be careful about interfering in a company's product design. No matter what happens, this case eventually will go to the Supreme Court, which is likely to want to put its own mark on the quintessential antitrust case of the Digital Age.

By Susan Garland in Washington