The firm hired Burson-Marsteller, the world's fifth-largest PR firm, to mount a quiet campaign to convince Internet companies, advertisers and regulators to oppose Google's takeover of the online advertising specialist, The Wall Street Journal and the London Observer reported.

In recent months, Burson pitched media outlets and Internet companies, alleging the deal was part of a larger discussion of "fair and free competition" in Internet-search and privacy rights of consumers, the Journal said.

In Europe, Burson urged Internet companies to sign an online petition for a more "transparent and competitive Internet" and gave the companies usernames and passwords to log in to Web site www.i-comp.org, the Journal said.

The pitches did not disclose Burson -- a Young & Rubicam Inc. unit -- was working for Microsoft, Google's largest rival, the newspaper said.

Burson Executive Vice President Josh Gottheimer said the firm was hired by Microsoft to set up i-comp.org as a "discussion forum" for issues of privacy and competition.

A Google spokesman would not comment on the campaign and said the DoubleClick deal was "positive for users and advertisers and fosters competition."