The FBI and the Energy Department bungled the investigation of a nuclear scientist suspected of giving China secret information about the design of the W-88 warhead, America's most advanced nuclear weapon, a Senate committee said yesterday.

The bipartisan report by the Senate Committee on Governmental Affairs says the investigators failed to look into other suspects, fought among themselves over a search warrant to a computer, and made other "compound missteps." As a result, the truth of what happened at Los Alamos National Laboratory may never be known.

The Chinese American scientist at the heart of the investigation, Wen Ho Lee, has been fired from his job at Los Alamos for an alleged security breach, but the Justice Department is still trying to determine whether to charge him with a crime. And the 32-page Senate report notes that it is still unclear whether any secrets really were stolen.

"We take no position in this document on whether W-88 or other nuclear weapons information was in fact compromised, or by whose hand this may have occurred," the committee wrote.

Some members of Congress have charged for months that China stole classified data from America's national laboratories, and that the Clinton administration dragged its feet after being alerted in 1997 to the espionage, which allegedly took place throughout the 1980s and '90s. The allegations, combined with NATO's accidental bombing of the Chinese Embassy in Yugoslavia, have seriously strained U.S.-Chinese relations.

The Senate report contains some disclosures that are damaging to Wen Ho Lee and others that appear to bolster his assertion of innocence.

The report discloses that Lee failed a polygraph test early this year in which he was asked whether he had passed nuclear secrets "to any unauthorized person." It also reveals that Lee and his wife, a secretary at Los Alamos, were already the subjects of an FBI security investigation when Energy Department investigators focused on them in late 1995 as the possible source of Chinese data on the W-88.

According to the committee, the FBI had "in the early 1990s" begun an inquiry based on information could reasonably be interpreted to indicate that Lee had provided significant assistance to" China. Neither the FBI nor the committee chairman, Sen. Fred Thompson (R-Tenn.), would comment yesterday on what that information was.

The report quotes a Department of Justice memo as saying the investigation of the alleged theft of information on the W-88 was "flawed from the start" because the FBI and the Energy Department had "multiple suspects" but quickly focused on Wen Ho Lee and his wife, Sylvia Lee, ignoring the others until much later.

At least some of the other suspects worked at Los Alamos, had access to secret information, were Chinese American, had traveled to China, and had made contact with visiting Chinese delegations, all of the elements that cast suspicion on the Lees, the report says.

However, the report notes one bit of information that might also have pointed investigators toward the couple: the FBI obtained a 1987 note, on the letterhead of a Chinese nuclear weapons institute, indicating that Sylvia Lee had requested that three Los Alamos documents be sent to the institute's deputy director "if they are unclassified."

A large section of the committee report focuses on two years of infighting between the FBI and the Justice Department over a warrant to search Lee's computer. The FBI repeatedly requested a warrant, but the Justice Department said it did not have sufficient information to justify one.

According to the committee, Lee had signed a waiver allowing his computer to be searched, but the FBI did not know about the waiver, because an Energy Department counterintelligence officer had given the bureau misleading information. At the same time, the report says, the FBI field agent failed to pass information about the computer search to his superiors and allowed months to pass before following up on inquiries.

When investigators finally combed through Lee's office computer last March, they found that he had transferred top-secret files from Los Alamos's classified computer system to the unclassified computer on his desk. It is still unknown, however, whether anyone outside the lab got access to the files.

One possible outcome of the Senate report, according to Thompson and the committee's ranking Democrat, Sen. Joseph I. Lieberman (Conn.), is that Congress may revise the law on such searches. Lieberman said he believes Congress should consider lowering the legal barriers for searches and surveillance in cases involving secrets of "huge significance," such as nuclear weapons.