A federal judge has given the government permission to privately brief her on what it considers the national security risks in releasing certain classified information in a high-profile leak prosecution involving a Fox News report.

Some legal experts on the handling of classified information said the decision this week ignores the law and lets the government put the defendant, former State Department arms expert Stephen J. Kim, at a disadvantage in preparing for trial. As Kim seeks the judge’s approval to use some of this information in his defense, the government already will have made secret arguments for why the material is so sensitive.

“The government can give the judge an entire parade of horribles of what will happen, and then the defendant is left fighting with one hand behind his back,” said Edward B. MacMahon, a lawyer who is representing a former CIA official in another leak case. “Using that process unfairly alters the playing field in a way that I don’t think [the law] contemplates.”

The order was issued Monday by U.S. District Judge Colleen Kollar-Kotelly, a former chief judge of a top-secret surveillance court who also authorized the National Security Agency to collect the phone call records of millions of Americans.

Kim is fighting charges that he illegally disclosed national defense information to Fox News correspondent James Rosen, who wrote an article about the North Korean nuclear program in 2009.

Federal prosecutors and Kim’s attorney, Abbe D. Lowell, are engaged in pretrial battles over which pieces of classified information are relevant and admissible at the trial, scheduled for April.

The statute in question is known as the Classified Information Procedures Act and governs how a defendant can use classified information at trial. A defendant must prove that the information is relevant and helpful to his case. The judge has to balance the defendant’s right to a fair trial and the government’s need to protect classified information.

Lowell said in court papers that the government is not allowed to rely on “secret evidence and secret arguments” when challenging a defendant’s right to use the information.

When the government prosecutes leak cases, it runs the risk of disclosing additional sensitive information. Federal prosecutors said in court filings that the government wants to “avoid divulging privileged information to the defendant, to which he is not otherwise entitled.”

Although the law does not explicitly provide for such “ex parte” briefings, Kollar-Kotelly agreed with the government’s analysis that such proceedings “are not prohibited at this stage by the text of the statute.” The judge noted that her decision applies narrowly to a subset of documents and is not a “blanket statement.”

John Cline, a San Francisco-based lawyer, disagreed with the judge’s interpretation. Cline, who represented then-Vice President Richard B. Cheney’s chief of staff, I. Lewis “Scooter” Libby, at his perjury trial, said this step in the proceedings is intended to be a full-throated adversarial process in which both sides have access to all the material, including government arguments.

Both Cline and MacMahon took issue with the government’s assertion of a classified-information privilege in a criminal case.

Defense attorney David H. Laufman, a former national security prosecutor, said that both parties had made valid arguments. But he said that Kollar-Kotelly’s narrowly tailored opinion probably would be upheld on appeal, particularly because it does not open a “broad new avenue the government can travel down in every case.”