The other two judges were harder to read. Chief Judge William Byrd Traxler Jr. said relatively little throughout the hearing, and the third jurist, Albert Diaz, asked skeptical questions of both sides.

The former C.I.A. officer, Jeffrey Sterling, is accused of leaking government secrets to Mr. Risen for his 2006 book, “State of War.” It recounted an effort by the C.I.A. a dozen years ago to sabotage Iranian nuclear research — an operation that the book portrays as having been dangerously botched. Mr. Risen is also a Pulitzer Prize-winning investigative reporter for The New York Times.

The Justice Department has tried to force Mr. Risen to testify, first during a grand jury proceeding and then again after Mr. Sterling was charged with leaking government secrets. But Mr. Risen has refused to identify his confidential sources, citing the First Amendment.

Last year, the trial judge overseeing the case, Leonie M. Brinkema of the United States District Court in Alexandria, Va., ruled that Mr. Risen was protected by a qualified “reporter’s privilege” that allowed her to balance whether it was necessary to force him to disclose his sources. Judge Brinkema contended that Mr. Risen’s testimony was not crucial because prosecutors could use other evidence against Mr. Sterling.

But the government has appealed that ruling, arguing that no reporter’s privilege exists in criminal trials. Mr. Parker on Friday invoked a 1972 Supreme Court case holding that there is no reporter’s privilege against being forced to testify before a grand jury. He said the case was “clear” that the same rule should apply in a trial.

But Judge Diaz pronounced the precedent “clear as mud.” Among other problems, the fifth vote in the majority for that case came from a justice who wrote his own concurring opinion that appeared to give a broader reading of press freedoms than the other four.

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A lawyer for Mr. Risen, Joel Kurtzberg, told the panel that no federal appeals court has adopted an understanding of First Amendment press protections as limited as the prosecutors’ view, urging them “not to accept the government’s invitation to be the first.”

A diverse coalition of more than two dozen media organizations, including The Times and Fox News, has filed a friend-of-the-court brief arguing that a qualified reporter’s privilege — allowing judges to protect reporters from testifying under some circumstances — is crucial for the “dissemination of news and information to the public.”

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There is a possibility that the appeals court will invoke a technicality to sidestep the need to directly address the novel First Amendment questions raised by the case — at least for now. Mr. Kurtzberg argued that the appeals court lacks jurisdiction to review Judge Brinkema’s order at this stage because the judge has said she will revisit the question of Mr. Risen’s testimony midway through the trial.

Both Judge Diaz and Judge Traxler asked questions about the jurisdictional matter. But Mr. Parker voiced doubt that Judge Brinkema will change her mind and argued that the appeals court should rule on the issue now. Prosecutors need to know whether they can invoke Mr. Risen’s testimony in opening statements, he said, and it would be too late for prosecutors to appeal again once a jury is seated.

A lawyer for Mr. Sterling told the court that his client took no position in the dispute between Mr. Risen and prosecutors.

The names of the three appeals court judges assigned to the case were not disclosed until Friday, as is the Fourth Circuit’s practice. All three were selected by Democrats: President Obama appointed Judge Diaz and President Bill Clinton appointed Judges Traxler and Gregory, although Judge Gregory received a recess appointment and was reappointed by President George W. Bush.

Mr. Sterling is one of six current and former government employees to be charged with leaking government secrets under the Obama administration — more such cases than were brought under all previous presidents combined.

Only the first half of the hearing was open to the public. Prosecutors are also appealing two other decisions by Judge Brinkema, including one barring them from using two witnesses because prosecutors missed a deadline for giving the defense team information that could be used to call their testimony into question. The discussion of the other portions of the case were closed to the public because they were expected to involve classified information.

Prosecutors have said that Judge Brinkema’s rulings, if they stand, “effectively terminated the prosecution” of Mr. Sterling.