The government wants to know, specifically, how often pornography or pornographic terms are searched for on the site.
Alberto Gonzales, in his official capacity as attorney general, filed suit in a San Jose court on the 18th of January to compel compliance with a subpoena.
But Google, according to the San Jose Mercury News, opposes releasing this kind of information to the government. A federal court in Pennsylvania is currently deliberating over the provisions of the contested 1998 Child Online Protection Act.