Mr. Holder repeated assertions by several Obama administration officials about the damage done by the cable disclosures, which began late last month.

“The national security of the United States has been put at risk; the lives of people who work for the American people have been put at risk; the American people themselves have been put at risk by these actions that are, I believe, arrogant, misguided and ultimately not helpful in any way,” Mr. Holder said.

Justice Department prosecutors have been struggling to find a way to indict Mr. Assange since July, when WikiLeaks made public documents on the war in Afghanistan. But while it is clearly illegal for a government official with a security clearance to give a classified document to WikiLeaks, it is far from clear that it is illegal for the organization to make it public.

The Justice Department has considered trying to indict Mr. Assange under the Espionage Act, which has never been successfully used to prosecute a third-party recipient of a leak. Some lawmakers have suggested accusing WikiLeaks of receiving stolen government property, but experts said Monday that would also pose difficulties.

Perhaps in a warning shot of sorts, WikiLeaks on Monday released a cable from early last year listing sites around the world  from hydroelectric dams in Canada to vaccine factories in Denmark  that are considered crucial to American national security.

Nearly all the facilities listed in the document, including undersea cables, oil pipelines and power plants, could be identified by Internet searches. But the disclosure prompted headlines in Europe and a new denunciation from the State Department, which said in a statement that “releasing such information amounts to giving a targeting list to groups like Al Qaeda.”

Asked later about the cable, Secretary of State Hillary Rodham Clinton said the continuing disclosures posed “real concerns, and even potential damage to our friends and partners around the world.”