UPDATE 1-Antitrust gripes prompt Vista changes-source

(Adds background, no comment from Microsoft, changes dateline, previous WASHINGTON)

CHICAGO, June 19 (Reuters) - Microsoft Corp. (MSFT.O) has agreed to modify its new Vista operating system in response to complaints that its desktop search function puts Google Inc. (GOOG.O) and other potential competitors at a disadvantage, a source familiar with the case told Reuters on Tuesday.

The U.S. Justice Department and Microsoft are expected to provide details of the proposed changes in a joint report filed in federal court later on Tuesday, the source said, speaking on condition of anonymity.

The source provided no details on what changes Microsoft had agreed to make.

A spokesman for Microsoft had no immediate comment.

In a complaint filed with the Justice Department in December, Google said a feature built into Microsoft's Windows Vista operating system that allows users to search a computer's hard drive did not leave room for competition from other desktop search applications.

Google contends that feature violates the consent decree that monitors Microsoft's conduct as part of its settlement with the U.S. government in its landmark antitrust case against the company.

The New York Times reported earlier in June that some state officials were alarmed by Google's complaint. But the newspaper said the Justice Department's antitrust chief had backed Microsoft and urged them to reject Google's complaint.

Microsoft has said it did not believe it had run afoul of the antitrust settlement.