Four U.S. consumer groups criticized Microsoft Corp.'s Windows XP operating system on Tuesday, saying the software giant was again using the anti-competitive tactics that have tied it up in court for three years.

In a joint statement, the Consumer Federation of America, Consumers Union, Media Access Project, and U.S. Public Interest Research Group, complained that the new operating system ''advances the company's illegal anti-competitive practices and harms the nation's consumers.''

``Activities such as communications, commerce, streaming audio/visual applications, and on-line services are, at the present, vigorously competitive,'' the groups said in a statement. ``These essential areas of the 21st Century economy will be threatened, and consumers harmed, if Windows XP and its tightly bundled version of Internet software hits shelves as planned.''

Microsoft spokesman Jim Desler denied the accusation. Windows XP, which is due for release on Oct. 25, ``is a product that offers great benefits for consumers and is critically important to the computer industry,'' he said.

The complaint from the consumer groups comes less than a week after attorneys general of Vermont and five other states added their support to the government's antitrust case and also expressed concerns about how Windows XP will affect competition in the software industry.

In a related development, a spokeswoman for the Justice Department confirmed on Tuesday that antitrust regulators from the United States and Europe briefed each other on their respective Microsoft antitrust cases during meetings in Washington on Monday.

European regulators are pursuing an investigation separate from the U.S. case, focused on whether Microsoft has tried to monopolize the market for computer servers and media-playing software.

The consumer groups, meanwhile, said they will outline their objections to Windows XP at a press conference scheduled for Wednesday, along with their proposal for sanctions against Microsoft.

U.S. District Court Judge Colleen Kollar-Kotelly is expected to hold hearings early next year to determine what remedies should be imposed on Microsoft to prevent future antitrust violations. Some state attorneys general have expressed concerns that some of the features in the new operating system, such as a media player and instant messaging, could hurt competition in the software business.