US federal and state regulators are expected to announce today antitrust action against Microsoft, one of the biggest such cases in history, rivalling the break-up of Standard Oil and telephone giant AT&T Corp.

The case would pit Microsoft founder Mr Bill Gates, against the full weight of the United States government, led by a determined chief justice department trustbuster, Mr Joel Klein.

The move is expected to be announced at a joint news conference with attorney-general Ms Janet Reno, assistant attorney-general Mr Klein and a few state attorneys general from the 19 or more involved.

It will come one day before Microsoft is scheduled to ship its Windows 98 operating system software to computer manufacturers for release on June 25th.

The government will allege that Microsoft, like other alleged monopolists before it, abused its power to compete unfairly and drive rivals from the marketplace.

The expected move comes after Microsoft had a favourable ruling in an appeals court which cleared the way for distribution of its Windows 98 software. In more good news for the company one state attorney-general pulled back from the rush to sue the company.

Experts say the nation's trustbusters can expect a bruising war against a powerful, battle-hardened company that has successfully fought competitors and the government for years.

The states and the justice department are likely to file different kinds of cases the in the US district court in Washington.