Google Inc. is poised to make voluntary concessions that will end a 20-month U.S. antitrust probe of its business practices without any enforcement action, two people familiar with the matter said.

Google, which has been under investigation by the Federal Trade Commission, is preparing a letter promising not to copy content from rival websites without permission and to allow advertisers to compare Google's ad-campaign data with performance on other Internet search engines, one of the people said Dec. 16. That will close the investigation without a lawsuit or settlement, said the people, who asked not to be identified because the matter isn't public.

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An end to the probe without any enforcement action would be a blow to Google's competitors including Microsoft Corp., Yelp Inc. and Expedia Inc., which formed an alliance to press the agency to act. They claim Google's dominance of Internet search, combined with favoring its own services in answers to queries, violates antitrust laws and impedes competition.

Adam Kovacevich, a Google spokesman, declined to comment on whether Google is preparing to announce concessions or any matters involving the FTC.

Cecelia Prewett, a spokeswoman for the FTC, also declined to comment.