The Obama Administration fought to keep a search warrant for James Rosen’s private e-mail account secret, arguing to a federal judge that the government might need to monitor the account for a lengthy period of time.

The new details are revealed in a court filing detailing a back and forth between the Justice Department and the federal judges who oversaw the request to search a Gmail account belonging to Rosen, a reporter for Fox News. A 2009 article Rosen had written about North Korea sparked an investigation; Ronald C. Machen, Jr., the U.S. Attorney who is prosecuting Stephen Jin-Woo Kim, a former State Department adviser who allegedly leaked classified information to Rosen, insisted that the reporter should not be notified of the search and seizure of his e-mails, even after a lengthy delay.

E-mails, Machen wrote, “are commonly used by subjects or targets of the criminal investigation at issue, and the e-mail evidence derived from those compelled disclosures frequently forms the core of the Government’s evidence supporting criminal charges.”

He argued that disclosure of the search warrant would preclude the government from monitoring the account, should such a step become necessary in the investigation. Machen added that “some investigations are continued for many years because, while the evidence is not yet sufficient to bring charges, it is sufficient to have identified criminal subjects and/or criminal activity serious enough to justify continuation of the investigation.”

Machen insisted the investigation would be compromised if Rosen was informed of the warrant, and also asked the court to order Google not to notify Rosen that the company had handed over Rosen’s e-mails to the government. Rosen, according to recent reports, did not learn that the government seized his e-mail records until it was reported in the Washington Post last week.

The new details indicate that the government wanted the option to search Rosen’s e-mails repeatedly if the F.B.I. found further evidence implicating the reporter in what prosecutors argued was a conspiracy to commit espionage.

According to recently unsealed documents in the case, the Obama Justice Department sought an extensive amount of information from Rosen’s e-mail account. In addition to Rosen’s correspondence with Kim, the government wanted to know about Rosen’s contacts with other government officials, including “records or information relating to the Author’s communication with any other source or potential source of the information disclosed in the Article.”

The government, which accused Rosen of being an “aider, abettor, and/or co-conspirator” in the Kim case, cast a wide net in its search of Rosen’s e-mail. Among other things, the search warrant requested access to:

—“Records or information related to Stephen Kim’s or the Author’s knowledge of laws, regulations, rules and/or procedures prohibiting the unauthorized disclosure of national defense or classified information.” —“Any classified document, image, record, or information, and any communications concerning such documents, images, records, or information.” —“Any document, image, record, or information concerning the national defense, including but not limited to documents, maps, plans, diagrams, guides, manuals, and other Department of Defense, U.S. military, and/or weapons material, as well as sources and methods of intelligence gathering, and any communications concerning such documents, images, records, or information.” —“Records or information related to the state of mind of any individuals seeking the disclosure or receipt of classified, intelligence and/or national defense information.”

In addition, the Justice Department searched the account for any Internet services Rosen may have accessed and records of “data transfer volume,” suggesting the government was looking for evidence that Rosen downloaded large quantities of potentially classified information.

The new documents show that two judges separately declared that the Justice Department was required to notify Rosen of the search warrant, even if the notification came after a delay. Otherwise: “The subscriber therefore will never know, by being provided a copy of the warrant, for example, that the government secured a warrant and searched the contents of her e-mail account,” Judge John M. Facciola wrote in an opinion rejecting the Obama Administration’s argument.

Machen appealed that decision, and in September, 2010, Royce C. Lamberth, the chief judge in the Federal District Court for the District of Columbia, granted Machen’s request to overturn the order of the two judges.

Rosen was not indicted in the case. Kim was indicted for making unauthorized disclosures of national defense information and for making false statements to F.B.I. agents about his contacts with Rosen.

Yesterday, hours after President Obama said, in a speech at National Defense University, that he had asked Attorney General Eric Holder to review the Justice Department’s policies concerning investigations of the media, NBC News reported that the warrant to search Rosen’s e-mail account was personally approved by Holder.