NEGOTIATIONS between Micro-soft and US government lawyers aimed at averting anti-monopoly lawsuits collapsed at the weekend, putting the Justice Department and at least 20 states back on a collision course with the world's most powerful software company.

The Justice Department said talks, which broke up at midday on Saturday, were not expected to resume. The government and the states are expected to file two separate but similar federal anti-monopoly lawsuits this morning.

Federal lawyers and state attorneys-general contend that Micro-soft, whose Windows software is used on virtually all desktop computers, illegally used its market power to suffocate competition, especially for Internet browsers.

A person familiar with the negotiations said the Justice Department and states wanted Microsoft to hide the screen that customers use to access Windows, called its interface; hide ways that consumers could use Microsoft's Internet browser, included in Windows, to view information on the World Wide Web; and include a copy of rival Netscape Communications Corp's browser in every version of Windows sold.

Microsoft accused the government of making ''unreasonable demands''.

Before the negotiations, Microsoft had launched an unprecedented campaign to sway public opinion and pressure states and the Justice Department against an anti-monopoly case.