After years in the shadows as an intelligence analyst and federal bureaucrat, Notra Trulock III pulled his chair up to the witness table in the Senate Armed Services Committee's vast hearing room and readied himself for a new role: whistleblower.

It was April, and the press had been full of his exploits for weeks as leaked reports of Chinese nuclear spying at Los Alamos National Laboratory dominated political debate in Washington. Leading Republicans in Congress were accusing the Clinton administration of dragging its feet.

And Trulock, in his first public testimony, backed up the charge.

Staring at the senators arrayed before him on the dais, Trulock said, without batting an eye, that his superiors in the Department of Energy "urged me to cover up and bury this case."

Soon, he was the talk of the town, telling the same shocking tale on NBC's "Meet the Press" one Sunday morning in May, when he compared the possible loss of secrets at Los Alamos to "the Rosenberg-Fuchs compromise of the Manhattan Project information" at the end of World War II.

But all that seemed like ancient history last week when Trulock, 51, abruptly resigned his $125,900-a-year post as the Energy Department's deputy director of intelligence amid growing controversy about his role in the espionage probe--and whether China had actually stolen secrets from Los Alamos.

"He was the golden boy for a while," said Robert S. Norris, a nuclear weapons expert at the Natural Resources Defense Council. "But now it looks like he's a little bit tarnished. We're no closer to actually knowing whether espionage was committed at all."

To his supporters, Trulock remains a courageous whistleblower who doggedly pursued evidence of Chinese espionage and remains almost single-handedly responsible for triggering the first real security and counterintelligence reforms at the weapons labs in 20 years. Rep. Christopher Cox (R-Calif.), whose House select committee on Chinese espionage was highly influenced by Trulock's secret testimony about China's theft of warhead design information, last week lauded his "valuable contributions."

But Trulock's detractors tell a far different story, describing him as a dangerous demagogue who built an espionage case at Los Alamos without solid evidence and singled out physicist Wen Ho Lee as the prime suspect largely because he is Chinese American.

"He's the great impostor, the great impostor," said one senior Energy Department official who clashed early on with Trulock. "He got a job and he pulled it off for three or four years--and it's finally caught up with him. He got what he wanted--his moment on the stage. He was the star of the show. That's what he lived for."

Trulock denied seeking the limelight. "I was thrust into it, kicking and screaming," he said in an interview after his resignation.

He also flatly denied singling out Wen Ho Lee as a suspect because he is Chinese American, as three officials involved in the investigation have charged in recent weeks. Trulock's supporters say that because the Chinese intelligence service targets overseas ethnic Chinese for espionage, taking Lee's ethnic background into consideration was legitimate.

The case began, Trulock said, when he and his staff wrote a 38-page report in spring 1996 on their "administrative inquiry" naming 12 possible suspects at several weapons facilities, three of whom were Chinese Americans. Trulock said he always assumed the FBI would use the document to investigate all 12.

"It was the FBI, pure and simple, who fingered Wen Ho Lee," he said. "I'm not about to say Wen Ho Lee did it. I never did say that."

Asked what he now believes to have been the extent of China's nuclear spying, Trulock made no comparison to the Rosenbergs, pointing instead to an analysis produced in April by the CIA and other members of the U.S. intelligence community as the best assessment of all. Its conclusion:

"China obtained by espionage classified U.S. nuclear weapons information that probably accelerated its program to develop future nuclear weapons. . . . We cannot determine the full extent of weapon information obtained. . . . We do not know whether any weapon design documentation or blueprints were acquired."

Trulock grew up the son of an Indianapolis fireman, graduated from Indiana University in 1970 and went off to work at the super-secret National Security Agency as an Army enlisted man.

With the Russian language training he received at Fort Meade, he became an analyst of Soviet military doctrine, worked at several Washington area defense contractors and landed an analyst's job at Los Alamos in 1990.

In 1993, after receiving awards from Los Alamos and the intelligence community, he transferred to Energy Department headquarters. In a year, he became director of the department's Office of Intelligence, even though he had no management experience and no counterintelligence training.

He soon became obsessed with Chinese espionage after the CIA obtained a document in 1995 indicating that China somehow had obtained classified information about the design of the newest U.S. W-88 warhead.

Determined to catch a spy and plug the security leaks, Trulock fought bruising bureaucratic battles--and ultimately won the day. A presidential decision directive issued by President Clinton in February 1998 mandated nearly all of Trulock's desired reforms.

But Trulock's posture changed at some point last year, around the time he appeared as a secret witness before Cox's panel. Trulock the inside intelligence analyst and reformer had become Trulock the whistleblower.

The transformation was complete by early spring, as he testified on Capitol Hill and graced the Sunday morning talk shows. One official who remembers him from Los Alamos as an extremely sharp Russian military analyst could hardly believe the transformation.

"He has become a political football," the official said.

As the spy scandal broke, Trulock emerged as the hero. Energy Secretary Bill Richardson immediately responded to Republican allegations of foot-dragging by firing Lee in March for security violations, identifying the nuclear physicist as the government's prime espionage suspect. Despite criticism inside the department of Trulock's methods, Richardson gave him a $10,000 bonus.

But events started to turn in June when a panel of the President's Foreign Intelligence Advisory Board, chaired by former senator Warren B. Rudman (R-N.H.), issued a report questioning the extent of any loss to espionage and criticizing Trulock and FBI agents for focusing on Lee in the absence of any hard evidence that he was the source of nuclear secrets somehow obtained by the Chinese. The report recommended that Trulock's office be disbanded and that its responsibilities be given to the CIA.

Lee has denied passing secrets to China and has not been charged with any crime.

Trulock's ego and slashing style were never more evident, his critics say, than in a letter of protest he fired off to Rudman, writing that he was "dismayed" and "deeply offended by your characterization of our efforts to uncover the depth and magnitude of this scandal."

Rudman fired back: "Your tone is both inflammatory and defensive. Even more disappointing are your wildly inaccurate assertions and reckless accusations. Altogether, your letter is wholly unbecoming of a responsible federal official addressing the work of an independent panel of the Executive Office of the President."

The most dramatic turnabout, however, occurred just two weeks ago when Robert S. Vrooman, Los Alamos's former counterintelligence chief, accused Trulock and FBI agents of singling out Lee largely because he was Chinese American. The case, Vrooman said, was "built on thin air." Two other officials soon came forward with similar accounts.

Trulock says Vrooman was merely trying to deflect blame from himself, following a recommendation by Richardson that Vrooman and two other lab officials be disciplined for mishandling the Lee investigation.

"Vrooman didn't do his job," Trulock said.

But he agreed that it was unfair for the department's inspector general to blame three lab employees in a recent report for mishandling the Lee case without holding any higher-ups in the Clinton administration accountable for security failures throughout the nation's nuclear weapons complex.

Indeed, Trulock said he decided to resign and take a program manager's job at TRW Inc., a major defense and intelligence contractor, after the IG's "whitewash," which also concluded that there was insufficient evidence to substantiate Trulock's charge that Elizabeth A. Moler, a former deputy secretary of energy, tried to block him from testifying before Congress last year.

When he read that, Trulock recalled, "I said these people are not serious--and I'm not wasting my time here anymore."

By last week, Trulock, who was considered a non-ideologue during his days at Los Alamos, declared himself a regular visitor to a chat room of FreeRepublic.com, one of the most conservative Web sites. "I have been lurking here for months," he messaged a group that was bitterly commenting on The Washington Post's treatment of his resignation. "During some of the most trying times, FR has been a source of moral support."

Shortly before leaving, Trulock sat down in his office at Energy Department headquarters and typed out a long "goodbye" e-mail to his staff. It was vintage Trulock, sad in tone but prideful and ever defiant.

"Your hard work put this office on the intelligence map," Trulock wrote. "The proof of your work can be seen in the various perverse recommendations to disband the office."

He evinced nothing but scorn for his bosses inside the department, who want to go on "pandering to the labs and the political appointees." But he counseled those he was leaving behind: "Don't be discouraged. This too shall pass."

CAPTION: Energy Secretary Bill Richardson applauds at May ceremony for Notra Trulock, then deputy director of intelligence.