Washington ? The North Korean government has acknowledged for the first time that it secretly has been developing nuclear weapons for years in violation of international agreements and has built “more powerful” weapons, as well, Bush administration officials said Wednesday night.

The North Koreans, who notified U.S. officials of the nuclear program earlier this month during talks in Pyongyang, the North Korean capital, said its existence nullifies a 1994 deal with the United States to halt their nuclear weapons effort in return for foreign help. One senior U.S. official said the new weapons project was a “very serious material breach” of the accord.

The Bush administration, stunned by the admission, dispatched envoys to the region Wednesday to consult with allies and called on North Korean leader Kim Jong Il to halt the weapons project. The administration also has begun consultations with Congress about what to do next, officials said.

“The United States is calling on North Korea to comply with all of its commitment under the Non-Proliferation Treaty and to eliminate its nuclear weapons program in a verifiable manner,” a U.S. official said. “What we seek is a peaceful resolution of this situation.”

The revelation thrust the Bush administration into an unexpected foreign policy crisis at a time when it is seeking to build international support for confronting Iraqi President Saddam Hussein and threatening to launch a military strike against Iraq if he refuses to disarm. The administration has said Saddam already possesses stockpiles of chemical and biological and is trying to develop a nuclear capability.

Administration officials Wednesday night offered mixed assessments of the implications of North Korea’s announcement. Some predicted it could lead to a possible military confrontation on the Korean peninsula; others said it could be a sign of a bid by North Korea to create an opening to the United States.

President Bush in January named North Korea a member of an “axis of evil,” along with Iraq and Iran.

Yet the announcement by the North Korean government comes amid a string of surprising moves by Kim, long criticized for peddling dangerous weapons and oppressing an impoverished population. In recent weeks, the Pyongyang government apologized for a naval battle with South Korea in the Yellow Sea and for the abduction of Japanese citizens in the 1970s.

‘Aggressive about it’

Briefing reporters by conference call, administration officials said North Korean Deputy Foreign Minister Kang Sok Joo offered no apologies when he informed U.S. officials of the covert nuclear weapons program during an Oct. 3-5 visit to Pyongyang. He was “assertive, aggressive about it,” one administration official said.

“It’s a very serious development if a country we had thought had entered into a serious and credible negotiation to retreat from a nuclear program in exchange for generous assistance” has violated that agreement, said Sen. Bob Graham, D-Fla., chairman of the Senate Intelligence Committee. “This is going to require a reassessment of our our commitments to North Korea.”

Extent unknown

Despite the North Korean announcement, the administration says it does not know the full extent of North Korea’s nuclear capabilities, nor do experts know for certain what Kang meant when he referred to more powerful weapons. Wednesday night, they said they assume he meant weapons of mass destruction, which typically include biological and chemical weapons.

North Korea’s new nuclear project relies on highly enriched uranium, while the nuclear effort that North Korea agreed to halt in the groundbreaking 1994 Agreed Framework was based on plutonium. U.S. officials would not answer when asked whether the highly enriched uranium had yet been turned into a weapon.

The CIA’s National Intelligence Estimate, released in December, reported that North Korea had likely produced one or two plutonium-based nuclear weapons by the mid-1990s.

For now, the administration is suspending its offer to engage North Korea a pledge of an economic and political opening in return for reductions in North Korea’s military posture and policies of weapons proliferation, along with an improvement in humanitarian conditions at home.

“In light of our concerns about the nuclear weapons program, we could not pursue that approach,” a U.S. official said during the conference call. “Everyone in the region has a stake in this issue, and no peaceful nation wants to see a nuclear-armed North Korea.”

The parallels between North Korea and Iraq are worth noting, said Henry Sokolski, executive director of the Non-Proliferation Education Center. He pointed to the administration’s repeated assertions that Iraq will not be secure until Saddam is removed from power.

“If we’re serious about Iraq, as we are and should be, we need to be twice as serious as we currently are about North Korea,” said Sokolski, who said he believed the administration should be tough on Kim. “If you’ve got a nuclear cheater, do you give them the benefit of the doubt and coddle him? Or do you say the burden’s on you to come clean?”