WASHINGTON  An unusual cast of conservatives has added momentum to a bill that would protect the confidentiality of reporters’ sources, even as the Bush administration has lobbied vigorously against the idea.

The latest flashpoint in the debate came Friday in an appellate courtroom in Washington, as a former reporter for USA Today faced fines of $5,000 a day for refusing to disclose the sources of her articles on the Federal Bureau of Investigation’s 2001 anthrax investigation.

A conservative judge on the United States Court of Appeals for the District of Columbia Circuit, Brett M. Kavanaugh, a former Bush White House official, offered perhaps the broadest defense of reporters’ rights during oral arguments in the case.

Judge Kavanaugh noted that “49 states have recognized some sort of common-law privilege” protecting the confidentiality of reporters’ relationships with their sources, and he questioned why lawyers for Toni Locy, the former USA Today reporter now facing a contempt citation, had not asserted that privilege more aggressively.