WASHINGTON (AFP) - A New York Times reporter has asked the US Supreme Court to block an order that would require him to reveal the confidential source for his book exposing CIA secrets.

In a brief filed on Monday, James Risen's lawyers said the case is a test of freedom of the press in investigating government misconduct.

"This case has been transformed into a potential constitutional showdown over the First Amendment and the role of the press in the United States because of the Obama Administration's aggressive use of the powers of the government to try to rein in independent national security reporting," Risen said in a statement to the Times' public editor Margaret Sullivan and published in the newspaper.

Risen blamed US President Barack Obama's White House for provoking "a basic constitutional fight over whether a reporter's privilege exists." And he insisted: "It is the Obama administration that wants to use this case and others like it to intimidate reporters and whistle blowers.

"But I am appealing to the Supreme Court because it is too dangerous to allow the government to conduct national security policy completely in the dark." Risen has been ordered to testify in the trial of former CIA officer Jeffrey Sterling, who is accused of disclosing confidential information of a secret operation against Iran.

Risen's 2006 book "State of War" contained information about what was described as a botched attempt by the CIA to have a former Russian scientist pass intentionally flawed nuclear blueprints to Iran to undermine its nuclear program.

"I fervently hope the court takes on his case and rules strongly in his favour," Sullivan wrote. "Mr Risen has said in the past that he is willing to go to jail rather than reveal the identity of his source."