WASHINGTON - John Walker Lindh, the American-born Taliban fighter who was captured in Afghanistan in November, pleaded guilty yesterday to two charges of aiding the terror-sponsoring regime in a surprise deal that lifted the threat of a life sentence.

The plea agreement, announced on the first day of what was to be a week of pretrial hearings in federal court in Alexandria, Va., carries a maximum 20-year prison term.

The chief prosecutor, U.S. Attorney Paul J. McNulty, called the plea agreement "an important victory for the American people."

He noted that under the deal, Lindh, 21, would fully cooperate with the U.S. investigation of al-Qaida and terrorism. He might, for example, be able to offer valuable information about other suspected terrorists and about al-Qaida.

The long hair and beard he wore in Afghanistan gone, the cleanshaven, short-haired Lindh told the judge: "I plead guilty. I plead guilty, sir."

The outline of the deal, which had been negotiated for weeks and up until midnight Sunday, was approved by President Bush. It was made known to the judge less than a half-hour before the start of yesterday's court session.

Instead of facing trial on 10 charges that carried at least three maximum life sentences, including conspiracy to kill Americans, Lindh pleaded guilty to two counts: aiding the Taliban and carrying explosives - a rifle and two grenades - while doing so.

Under the agreement, Lindh would serve up to two consecutive 10-year prison sentences and would have to cooperate with U.S. intelligence and anti-terrorism efforts.

"The court finds your plea of guilty to be knowing and voluntary," Judge T.S. Ellis III said. "The court accepts your plea and adjudges you now guilty."

Attorney General John Ashcroft applauded the deal, calling it "an important victory" in America's war on terrorism and an "appropriate outcome."

"By going to Afghanistan and fighting shoulder to shoulder alongside the Taliban, John Walker Lindh allied himself with terrorists who reject our values of freedom and democracy and turned his back on the United States of America," Ashcroft said in a statement.

"He will now spend the next 20 years in prison."

With his family seated behind him, Lindh, who grew up in wealthy Marin County, Calif., described his actions.

"I provided my services as a soldier to the Taliban last year, from about August to November," said Lindh. "During the course of doing so, I carried a rifle and two grenades."

Emotionally charged

Lindh's lead attorney, James J. Brosnahan, commended prosecutors for being "reasonable" and "professional," and said the deal represented for his client "a clearing of his situation."

He said he thought Lindh's case was hurt by the emotionally charged post-Sept. 11 "environment in which we're all living," one that he said would have made total exoneration difficult.

Lindh "was a soldier in the Taliban," Brosnahan said. "He did it for religious reasons. He did it as a Muslim."

Brosnahan noted with satisfaction that the government had dropped the charges that directly involved terrorism.

But McNulty, the U.S. attorney, said the plea deal amounted to Lindh's agreeing with "the heart" of the government's case against him - "that he allied himself with the Taliban, who, of course, are closely connected and associated with al-Qaida, a terrorist organization."

Incriminating words

With Lindh's trial set for Aug. 26, defense attorneys had intended to ask the judge to throw out statements Lindh made after his capture in Afghanistan. They argued that Lindh had not been informed of his constitutional rights to remain silent and have a lawyer present.

In those interviews - with CNN, with the FBI and with military officials - Lindh described his allegiance to the Taliban and claimed to have met Osama bin Laden, federal prosecutors said. But Lindh's lawyers said his statements were not credible because he had been malnourished, sleep-deprived, bound and blindfolded after he was taken into custody by Northern Alliance forces and later turned over to the U.S. military.

McNulty said he was confident that the government could have prevailed on all counts. But he said he saw the plea agreement as a chance to secure a "very tough sentence" and Lindh's future cooperation. He also said it saves the government from having to use money and resources in a high-profile terrorism trial.

Others noted that the plea deal also spares the government the risk of revealing sensitive information in an open trial.

"This case," McNulty said, "proves that the criminal justice system can be an effective tool in the fight against terrorism."

Under the deal, McNulty said, Lindh agreed to forgo any personal profit from his actions, with all proceeds from any sale of his story going to the federal government. Lindh has also withdrawn any claims of mistreatment by the U.S. military.

Lindh smiled broadly at his family as he arrived in the courtroom wearing a green prison jumpsuit yesterday, according to witnesses, but looked straight ahead as he was escorted out.

His father, Frank Lindh, said he was grateful that the government dropped the most serious charges. "I hope the government will come around even further and say that even 20 years is wrong for this boy."

'A good man'

He said he told his son after he was brought back to the United States that Nelson Mandela - "a good man, like John," he said - had served 26 years in prison. "And I told him to be prepared for something like that," Frank Lindh said.

He said his son expressed no bitterness about the United States or his treatment by the military. "John loves America, and we love America," he said.

The original 10-count indictment included conspiracy to murder Americans, among them Johnny M. "Mike" Spann, a CIA agent who was killed in a prison uprising. Spann had interrogated Lindh at a prison compound near Mazar-e Sharif in northern Afghanistan shortly before the deadly riot. That count was among those dropped in the plea agreement.

Family disappointed

Yesterday, members of Spann's family said they were disappointed by the deal.

"My son and all those who are serving overseas are let down by this decision," said his father, Johnny Spann. His mother, Gail Spann, said she believed Lindh could have saved her son's life by telling him that the prison riot was about to erupt and that his life was at risk.

Lindh's sentencing hearing is set for Oct. 4. He has asked to serve his time in a prison near his family in California, Brosnahan said.

The lawyer said his client, who converted to Islam as a teen-ager, wants to devote himself to study - Arabic and Islam, as well as U.S. and political history.