Still, several legal specialists in matters related to leaks of classified information say that prosecuting Mr. Assange or WikiLeaks on charges that they had violated the Espionage Act would face many hurdles, from the diplomatic difficulty in persuading a country to arrest and extradite Mr. Assange to an array of legal defenses he could mount if the United States managed to detain him. Mr. Assange is an Australian activist who has operated in various European cities.

Susan Buckley, a partner at the law firm Cahill Gordon & Reindel who specializes in communications law, said the Espionage Act had rarely been used and so there were few guides for how such a novel case would play out. For example, it is not clear whether the law applies to foreigners for actions overseas, although she noted that in a 1985 case, a judge ruled that the law did apply abroad.

It would also be highly unusual to use the law to go after the recipient and disseminator of a leak, rather than just the person who provided the information. Several scholars said they were aware of only one previous attempt to bring such a prosecution — the 2005 indictment of two former staff members of the American Israel Public Affairs Committee who were accused of passing on information about American policy toward Iran from a military analyst to Israel.

In 2009, prosecutors dropped the case after several court rulings that they said had sharply diminished the likelihood that they would win a conviction. But the Aipac case was controversial from the start, in part because it was seen as a step toward prosecuting journalists who write about classified matters, and a prosecution of Mr. Assange and WikiLeaks could also raise First Amendment issues.

A military spokesman noted that the Army had legal jurisdiction only over service members, and so any decision to prosecute WikiLeaks would be up to the Justice Department. A spokesman said the Justice Department would “not speculate on where the investigation may or may not lead or various other hypothetical scenarios.”

Mr. Assange has not said where he obtained the documents. But a military intelligence analyst, Pfc. Bradley Manning, has been charged with leaking other classified documents and videos that have appeared on the WikiLeaks Web site.

The disclosure of documents containing the names of Afghan informants, which was reported Tuesday in The Times of London, could further complicate the Obama administration’s efforts to manage the course of the war in Afghanistan.