Google has stepped up its battle to acquire advertising group DoubleClick, as the company's chief legal officer appeared before the US Congress yesterday.

David Drummond told the Senate hearing that the proposed $3.1bn deal would be beneficial to the public and US enterprise.

"Online advertising benefits consumers, promotes free speech, and helps small businesses succeed," said Drummond in a prepared statement.

"Google’s acquisition of DoubleClick will help advance these goals while protecting consumer privacy and enabling greater innovation, competition, and growth."

A subcommittee of the Senate Committee on the Judiciary will decide if the merger risks infringing on privacy and antitrust rules.

The attack on Google's planned purchase has been led by key rival Microsoft. The software giant's general counsel, Brad Smith, told the hearing that acquiring DoubleClick would make Google, "the overwhelmingly dominant pipeline for all forms of online advertising."

Google said that it has consulted several consumer and industry groups in an effort to respond to public concerns over privacy.