In November 2001, when the Bush administration was absorbed in the aftermath of the Sept. 11 terrorist attacks, intelligence analysts at the Lawrence Livermore National Laboratory completed a highly classified report and sent it to Washington. The report concluded that North Korea had begun construction of a plant to enrich uranium that could be used in nuclear weapons, according to administration and congressional sources.

The findings meant that North Korea was secretly circumventing a 1994 agreement with the United States in which it promised to freeze a nuclear weapons program. Under that deal, the North stopped producing plutonium.

Now, however, there was evidence that the North was embarking on a hidden quest for nuclear weapons down another path, using enriched uranium.

Although the report was hand-delivered to senior Bush administration officials, "no one focused on it because of 9/11," according to an official at Livermore, one of the nation's two nuclear weapons laboratories. An informed member of Congress offered the same conclusion.

The findings of the Livermore report were confirmed in a June 2002 National Intelligence Estimate, a major assessment by the CIA and all other intelligence agencies. These reports are part of a complex and hidden trail of intelligence about the North Korean effort that has raised questions about why the Bush administration waited until early October 2002 to confront officials in the capital, Pyongyang, with the intelligence -- and to go public several weeks later -- when details had been accumulating for more than two years.

The North Korean drive to enrich uranium came as the Bush administration was trying to build support for military action against Iraqi President Saddam Hussein on grounds he was hiding a program of weapons of mass destruction and would be more dangerous if he obtained nuclear weapons. Some critics say the Bush administration kept secret the most worrisome intelligence about a North Korean nuclear plant out of concern that public disclosure would undermine the campaign against Iraq, or interfere with the pursuit of Osama bin Laden and his network. Top administration officials have repeatedly denied that they suppressed the intelligence for political reasons.

Today, the administration faces new challenges as satellite data reportedly show North Korea moving fuel rods from a reactor site that was mothballed under the 1994 agreement. The site contains 8,000 such rods which, if reprocessed, could yield enough plutonium for about five bombs in approximately one month, according to Daniel A. Pinkston, senior research associate and Korea specialist at the Center for Nonproliferation Studies.

Moving the rods away from the storage site could make it much harder for outsiders to monitor whether North Korea was using them to build a bomb. Since 1994, the rods had been in storage under international monitoring, but recently the inspectors from the U.N.-chartered International Atomic Energy Agency were expelled from the country.

CIA analysts said they now believe North Korea is moving full speed toward building a weapon with plutonium. U.S. intelligence has never included firm evidence that North Korea actually possesses a bomb, although there has been speculation that it had one or more weapons. North Korea also has missiles that could be used to deliver a weapon, including between 500 and 600 missiles modified from the Soviet-built Scud, with relatively short ranges of 150 to 300 miles. Also, in 1993 North Korea tested a missile with an 800-mile range, which could reach Japan, and in 1998 launched a three-stage missile over Japan. One stage flew an estimated 3,450 miles before breaking up in the Pacific Ocean. The following year, North Korea announced a moratorium on missile tests, but recently threatened to resume them.

Pakistan Gave Plans

The history of the intelligence about North Korea's drive to enrich uranium underscores how the effort to stop weapons proliferation is made more complex by other foreign policy goals.

For example, the Livermore report included the disclosure that Pakistani scientists were the source of the plans showing the North Korean leader, Kim Jong Il, how uranium is enriched, the sources said.

Just weeks after the Sept. 11 attacks, Gen. Pervez Musharraf, Pakistan's president, joined the United States in the fight against bin Laden and the Taliban in neighboring Afghanistan. The United States, in return, dropped sanctions imposed on Pakistan for pursuing a nuclear program. According to one senior administration official, it was at this point that Musharraf's government provided some of the new intelligence about North Korea, and the Pakistani president took steps to close down the channel that had delivered the nuclear know-how to Pyongyang. Pakistan's leadership "wanted to show they were cooperating," said one senior official who was close to the situation.

The reasons the Bush administration did not act earlier on the information about North Korea are in dispute. Administration officials say the intelligence was fragmentary and unclear, but critics in Congress have questioned this. "The Bush administration rhetoric about North Korea has never been backed by action," said Rep. Edward J. Markey (D-Mass.), a leading congressional advocate of stronger measures to control weapons proliferation. Markey, along with Rep. Christopher Cox (R-Calif.) and recently retired Rep. Benjamin A. Gilman (R-N.Y.), have been pressing the administration for more than a year to take action on North Korea.

Under the 1994 agreement, known as the Agreed Framework, North Korea pledged to freeze a nuclear program that could produce plutonium at its Yongbyon plant. In exchange, the United States agreed to help build a light-water reactor to supply North Korea with electricity, and also to supply the country with fuel oil.

Then, in the late 1990s, the CIA and Defense Intelligence Agency began receiving sporadic reports suggesting that North Korea was attempting to bypass the '94 agreement by seeking technologies associated with enriching uranium for nuclear bombs.

Nuclear Program Reported

North Korea's nuclear weapons program dates to the late 1950s, just a few years after the United States secretly based nuclear bombs, and later nuclear artillery, in South Korea. Although the nuclear weapons were removed from South Korea in the 1970s, U.S. Navy ships and submarines in the area continued to carry them, pushing North Korea to develop a nuclear arsenal of its own, according to Morton H. Halperin, who worked on Korean nuclear matters in both the Carter and Clinton administrations and is currently with the Council on Foreign Relations. North Korean scientists were trained in the Soviet Union and China, among other places.

A recent study by the Congressional Research Service noted that "North Korea's secret uranium enrichment program appears to date from 1995 when North Korean and Pakistan reportedly agreed to trade North Korean Nodong missile technology for Pakistan uranium enrichment technology."

"The Clinton Administration reportedly learned of it in 1998 or 1999, and a Department of Energy report of 1999 cited evidence of the program," the study added.

Also, at the National Defense University, a 1999 study group chaired by Richard L. Armitage, now deputy secretary of state, and including Paul D. Wolfowitz, now deputy defense secretary, concluded that the 1994 agreement had frozen "only a portion of [North Korea's] nuclear program" and that Pyongyang was "seeking to develop a covert nuclear weapons program."

In November 1999, a House Republican advisory group that included the chairmen of the armed services, international relations and intelligence committees released a report that said of the North: "There is significant evidence [of] undeclared nuclear weapons development activity." The report specifically mentioned "efforts to acquire uranium enrichment technologies."

An unclassified version of a CIA report said, "During the second half of 1999, Pyongyang sought to procure technology worldwide that could have applications in its nuclear program, but we do not know of any procurement directly linked to the nuclear weapons program." A former senior official in the Clinton administration said the secret part of the report outlined details of purchases or attempts to gain assistance which were then believed to indicate an "experimental" or "research and development approach" to starting a uranium enrichment program.

In February 2000, President Clinton approved funds for North Korea under the '94 agreement. But he stopped short of a formal certification to Congress that "North Korea is not seeking to develop or acquire the capability to enrich uranium." Clinton waived the certification.

Over the next two years, reports on Pyongyang's nuclear-related purchases continued while the incoming Bush administration began a review of North Korean policy. Bush took a more hostile approach to North Korea than Clinton had, but the focus was on the missile threat and Bush's desire to build a missile defense system.

Sept. 11 Changed Focus

The focus abruptly changed after the Sept. 11 attacks. Bush ended sanctions against Pakistan and Musharraf provided new details of what had been given to North Korea.

A CIA classified report on weapons of mass destruction activities covering the last six months of 2001 and distributed to senior Bush policymakers reported: "The North has been seeking centrifuge-related materials in large quantities to support a uranium enrichment program. It also obtained equipment suitable for use in uranium feed and withdrawal systems."

In his State of the Union address a year ago, Bush labeled North Korea as part of an "axis of evil" that included Iran and Iraq. He described the North as "a regime arming with missiles and weapons of mass destruction while starving its citizens." He did not, however, mention the evidence of a uranium enrichment program.

Last March, Bush, like Clinton, refused to certify that North Korea was complying with the 1994 agreement in releasing another tranche of money. But Bush again did not bring up the secret uranium enrichment program, saying only that Pyongyang had hidden materials from International Atomic Energy Agency inspectors.

By May, the intelligence had grown more worrisome. According to sources, those within the government wanting to act on North Korea, including Vice President Cheney, pushed the National Intelligence Council to pull together a National Intelligence Estimate on whether the North was building the uranium enrichment facility. Henry D. Sokolski, who handled nonproliferation issues for Cheney when he was defense secretary during the first Bush administration and now directs the Nonproliferation Policy Education Center, said the National Intelligence Estimate was a major step the Clinton team had never attempted on North Korea.

Little Said in Public

But the administration's public stance was still vague. In a May 6 speech before the Heritage Foundation, John Bolton, the undersecretary of state for arms control and international security, focused on the "axis of evil" countries. Bolton was a fierce advocate inside the government for action against North Korea, but he only briefly mentioned that North Korea had a "covert" nuclear weapons program. Instead, he emphasized North Korea's effort to acquire "infectious agents, toxins and other crude biological weapons."

In June 2002, the intelligence community produced a National Intelligence Estimate that "conclusively" confirmed the North had turned from research and development to actual purchases of materials to construct a gas centrifuge facility to enrich uranium, according to a senior intelligence official. The highly classified report was first disclosed by reporter Seymour M. Hersh in the Jan. 27 issue of the New Yorker magazine.

According to congressional sources, the document was not sent to the House or Senate intelligence committees, which were only briefed months after it was finished.

Also, Markey and the other congressmen wrote to Bush about reports that had appeared in the South Korean press suggesting North Korea might have a new uranium enrichment program. In July, they received a reply from Bush's national security adviser, Condoleezza Rice, in which she made no mention of the National Intelligence Estimate. Instead, Rice said the United States is "committed to ending North Korea's nuclear weapons program" but added that Bush would continue to provide technology for the light-water reactors agreed to under the 1994 deal. Meanwhile, she added, Pyongyang had been told of Washington's "concerns" about its lack of full cooperation with International Atomic Energy Agency.

Halperin, who worked for the National Security Council in the Clinton administration and later headed policy planning at the State Department, said the Bush team "did not want to pay attention to North Korea because they knew there was no military option, knew they would have to negotiate as Clinton did, and so, they were in a box."

On July 31, Secretary of State Colin L. Powell had an unusual, private meeting with North Korea's foreign minister, Paek Nam Sun, while the two were in Brunei. Powell later said in an interview that he was aware of the NIE and other intelligence that "this enriched uranium program was going on. . . . Nevertheless, we wanted to move forward with the North Koreans."

On Aug. 26, Cheney made his first tough speech on Iraq, saying action had to be taken against Hussein and his government in part because "they continue to pursue the nuclear program they began so many years ago."

Three days later, speaking before a group of Korean War veterans, Cheney made only passing reference to North Korea as a country of "repression, scarcity and starvation." North Korea's nuclear weapons activities were never mentioned; Iraq took center stage. "On the nuclear question," Cheney said, "many of us are convinced that Saddam will acquire such weapons fairly soon."

Intelligence Report Not Cited

On that same day, Bolton, who sources said was also familiar with the NIE, gave a speech to the Korean-American Association in Seoul. He raised the North Korean leader's chemical and biological weapons programs. North Korea, he said, was "exerting its utmost efforts to produce chemical weapons" and "has one of the most robust offensive bioweapons programs on earth."

On the nuclear program, Bolton expressed concern about failure to allow IAEA inspectors to conduct required inspections under the '94 agreement. He did not mention the recently completed NIE. Instead, he quoted from a less specific document, the declassified CIA report sent Congress a year earlier, covering 1999, which said: "Pyongyang continued its attempts to procure technology worldwide that could have application in its nuclear program."

In the first week in October, Bush won agreement with House leaders for a congressional resolution authorizing the use of force in Iraq, with or without U.N. approval. Assistant Secretary of State James A. Kelly was sent to North Korea from Oct. 3 to 5 to confront it with what the United States had learned. During the trip, North Korea acknowledged the secret uranium facility. But Kelly did not reveal the startling news. It remained secret while Bush pressed Congress for approval of the Iraq resolution. Only after Congress had acted and Bush signed the resolution did the White House disclose, in mid-October, that North Korea had a uranium enrichment program.

Staff writer Joby Warrick contributed to this report.

Kim Jong Il reportedly received technology from Pakistan.Secretary of State Colin L. Powell met with North Korea's foreign minister, Paek Nam Sun, right, while the two were in Brunei last July 31. Powell later said that he was aware of the intelligence that "this enriched uranium program was going on."