FORT MEADE, Md. — A military judge on Tuesday found Pfc. Bradley Manning not guilty of “aiding the enemy” for his release of hundreds of thousands of military and diplomatic documents to WikiLeaks. But she convicted him of multiple counts of violating the Espionage Act, stealing government property and other charges that could result in a maximum sentence of 136 years.

In delivering the mixed verdict, the judge, Col. Denise Lind, pulled back from the government’s effort to create a precedent that press freedom specialists had warned could have broad consequences for the future of investigative journalism about national security in the Internet era.

Colonel Lind marched through a quick litany of the charges and specifications against Private Manning, 25, who stood quietly in his dress uniform as she spoke. She said she would issue findings later that would explain her ruling.

The sentencing phase in the court-martial will begin on Wednesday with more than 20 witnesses each for the prosecution and the defense. It could last weeks; there is no minimum sentence in the military justice system. Subsequent appeals could take years, legal specialists said.

Most reporters watched the proceedings from a closed-circuit feed in a filing center. One who was able to watch from inside the small courtroom here said Private Manning at first appeared relaxed when he entered the room, smiling and drinking from his water bottle. But as the hour drew near he grew more stoic, and he showed no emotion as Colonel Lind read her findings.

The aiding the enemy charge was the first in the list, and she said “not guilty.” But she quickly moved into a long list of guilty findings for the bulk of the remaining charges, including six counts of violating the Espionage Act, five of stealing government property, and one violation of the Computer Fraud and Abuse Act. Each of those carries up to a 10-year sentence. She also found Private Manning guilty of various lesser charges, including multiple counts of disobeying orders.

But Colonel Lind accepted his lesser guilty pleas on two counts, one of which involved leaking a video of an American helicopter attack in Baghdad that killed a group of men.

She also found him not guilty of the charge that he had leaked a video of an airstrike in Afghanistan in which numerous civilians had died in late 2009; Private Manning had admitted leaking it, but said he did so in the spring of 2010, after the date listed in the charge.

WikiLeaks, in a Twitter post, called the Espionage Act convictions “a very serious new precedent for supplying information to the press.”

Still, Yochai Benkler, a Harvard law professor who testified in Private Manning’s defense, praised the judge for making an “extremely important decision” to reject the aiding the enemy charge and thereby deny “the prosecution’s effort to launch the most dangerous assault on investigative journalism and the free press in the area of national security that we have seen in decades.”

But he said that the potential decades of imprisonment Private Manning still faces remains a major blow to “leakers and whistle-blowers,” and that the prospect of decades of imprisonment “is still too high a price for any democracy to demand of its whistle-blowers.”

Steve Aftergood, the director of the project on government secrecy for the Federation of American Scientists, called the outcome “a weighty verdict that the prosecution would count as a win,” but argued that the “larger significance of the case” may be limited.

“The unauthorized disclosures that Manning committed were completely unprecedented in their scope and volume,” he said. “Most investigative journalism does not involve the wholesale publication of confidential records, so the impact of these verdicts on working journalists may be confined. It’s not good news for journalism, but it’s not the end of the world either.”

Months before the trial, which began in June, Private Manning had already confessed to being WikiLeaks’ source for some 700,000 files that vaulted the organization into global fame three years ago. They included videos of airstrikes in which civilians were killed; front-line incident reports from the Afghanistan and Iraq wars; dossiers on men being held without trial at Guantánamo Bay, Cuba; and about 250,000 diplomatic cables.

But the government was determined to press forward with the more serious charges against him. Because most of the facts in the case were not in dispute, the trial raised the more abstract question of how to understand what Private Manning had done.

Throughout the trial, prosecutors sought to portray him as an “anarchist” and a “traitor” who recklessly endangered lives and betrayed his country out of a desire to “make a splash.” The defense portrayed him as a young, naïve, but good-intentioned humanist who wanted to prompt debate and who avoided releasing documents that could cause harm.

Hours before the verdict, about two dozen supporters of Private Manning gathered at the main gate to Fort Meade, some wearing T-shirts that said “truth.” They displayed signs to traffic with messages like “whistle-blowers keep us honest” and “thank you Bradley Manning.”

Ben Wizner, director of the Speech, Privacy and Technology Project for the American Civil Liberties Union, expressed relief that Private Manning was acquitted of the “most dangerous charge” brought against him, but criticized the espionage charges.

“While we’re relieved that Mr. Manning was acquitted of the most dangerous charge, the A.C.L.U. has long held the view that leaks to the press in the public interest should not be prosecuted under the Espionage Act,” he said. “Since Manning already pleaded guilty to charges of leaking information — which carry significant punishment — it seems clear that the government was seeking to intimidate anyone who might consider revealing valuable information in the future.”

Gregg Leslie, the legal defense director for the Reporters Committee for Freedom of the Press, said the Espionage Act convictions — a charge that covers not spying but releasing defense information that could cause harm — were not surprising but were still alarming, given that the information released was important for public debate.

“We always hate to see a government employee who was trying to publicize wrongdoing convicted of a crime, but this case was unusual from the start because of the scope of his release,” he said. “Because of Manning’s obligations as a government employee, it almost would have been more of a surprise if the government had not won on an Espionage Act count.”

Still, he added: “Whistle-blowers always know they are taking risks, and the more they reveal the bigger the threat is against them. But we know they are not betraying the government. And when they contribute vital information to an important public debate, it should not be a crime — especially the kind of crime that sends you to jail for the rest of your life.”

Private Manning is one of seven people who have been charged with leaking information to the press for public consumption under the Obama administration. Under all previous presidents combined, there were only three such cases.