BRUSSELS, Belgium — Microsoft Corp. is making several key changes to its forthcoming Windows Vista operating system in an attempt to soothe European antitrust worries, while keeping its worldwide distribution plans on schedule.

Brad Smith, Microsoft's general counsel, said yesterday the company agreed to change how people can set their preferred search service if they upgrade to Microsoft's new version of the Internet Explorer browser. The Redmond, Wash., company also has tweaked Vista's security system to address concerns that the system was favoring Microsoft's products over competing security offerings.

In addition, the company plans to have an international standards organization review a controversial new file format that will be included in Windows and the company's Office business suite. Smith said that is a step toward making the format available for other companies to license.

Even with the changes, which will be included in all versions the company ships worldwide, Microsoft said it still plans to deliver the long-delayed Vista to large businesses in November and consumers and small businesses in January.

The announcement follows many testy exchanges between Microsoft and European regulators, who are still embroiled in a long-running antitrust dispute over the current version of Windows.

But Smith told the Associated Press the changes announced yesterday were the result of conversation rather than litigation, between the two parties. EU antitrust chief Neelie Kroes and Steve Ballmer, Microsoft's chief executive, spoke by phone Thursday.

"When you have a constructive dialogue with people, you can actually figure out how to solve problems in a way that really wins for everybody," Smith said.

Still, he cautioned that the changes don't guarantee the company will be free of antitrust concerns in Europe or elsewhere.

The EU antitrust office, which warned this spring it had concerns about the new Windows software, refused to back Microsoft's optimism that European concerns had been met.

"The jury is out," EU spokesman Jonathan Todd said. "It is up to Microsoft to shoulder its own responsibility to ensure full compliance with competition rules."

He said the commission "will closely monitor the effects on the market and in particular examine any complaints."

Antitrust complaints often come up long after a product has been released, rather than in advance.

Microsoft also is hoping changes announced yesterday will resolve trade worries with South Korea, where the Korea Fair Trade Commission said Microsoft abused its dominant market position by tying certain software to Windows.

Vista will be the first major upgrade to Microsoft's flagship operating system since Windows XP was released in 2001. It touts a sleeker look, improved security features, better protection against spyware and viruses and more intuitive search tools to help users find saved files.