US antitrust officials this week accused Microsoft of engaging in a "broad anti-competitive campaign" to protect its monopoly in operating software that will last "well into the future" unless it is halted by the courts.

The Justice Department alongside 19 state attorneys-general said the landmark case against the world's largest software company had demonstrated "a broad pattern of unlawful conduct".

In legal submissions to Judge Thomas Jackson, the US government said Microsoft's industry-wide campaign had "the purpose and effect of thwarting emerging threats to its powerful and well entrenched operating system".

"Personal computers are locked into a Microsoft world, one in which a single company essentially controls the configuration of desktop computing," the government said.

The legal submissions are designed as a summary of the epic antitrust case to help Judge Jackson craft his so-called findings of fact. The judge is expected to rule on issues of fact including whether to define Microsoft as a monopoly in autumn.

Microsoft revealed the content of its rival submissions this week, arguing that the government had failed to prove any of its allegations of illegal conduct. It denied that the company exerts monopoly power over the computer industry.

Microsoft said on Tuesday: "While the government may have scored public relations points against the company in the initial phase of the trial using courtroom theatrics and bits of evidence out of context, we are entering a new phase of the case . . .

"An examination of the evidence the government has provided clearly shows that this case is largely a vehicle for Microsoft's competitors to attack Microsoft, rather than compete in the market place."

In their legal filings, antitrust officials said Microsoft had illegally used its market power to "squelch" the threat from so-called middle-ware software that runs on top of its Windows operating system, and which supports other applications.

The leading middle-ware threat was posed by Internet browsers developed by Netscape Communications, allowing computer users to read pages and run software from the World Wide Web.

As a result, Microsoft attempted to "curtail" other threats that supported middle-ware, such as Sun Microsystem's Java programming language and Internet technology developed by Intel and Apple Computer.

"It [Microsoft campaign] succeeded in preserving Microsoft's monopoly power by preventing the successful development of alternative platforms that could have eroded its Windows monopoly and given consumers greater choice," the government said.

Microsoft argues that consumers have not been harmed by its allegedly illegal actions, as Internet software is now distributed free.