WASHINGTON — Julian Assange, the flamboyant founder of WikiLeaks, is living on a supporter’s 600-acre estate outside London, where he has negotiated $1.7 million in book deals and regularly issues defiant statements about the antisecrecy group’s plans.

Meanwhile, the young soldier accused of leaking the secret documents that brought WikiLeaks and Mr. Assange to fame and notoriety is locked in a tiny cell at the Quantico Marine Corps Base in Virginia. The soldier, Pfc. Bradley Manning, who turned 23 last month in the military prison, is accused of the biggest leak of classified documents in American history. He awaits trial on charges that could put him in prison for 52 years, according to the Army.

Even as members of Congress denounce both men’s actions as criminal, the Justice Department is still looking for a charge it can press against Mr. Assange, demanding from Twitter the account records, credit card numbers and bank account information of several of his associates. Legal experts say there are many obstacles to a prosecution of the WikiLeaks founder, but one approach under consideration is to link the two men in a conspiracy to disclose classified material.

Accusations from supporters that Private Manning is being mistreated, perhaps to pressure him to testify against Mr. Assange, have rallied many on the political left to his defense. The assertions have even drawn the attention of the United Nations’ special rapporteur on torture, Juan E. Mendez, who said he had submitted a formal inquiry about the soldier’s treatment to the State Department.