A senior North Korean official, in an unusual visit to Capitol Hill sanctioned by the Bush administration, said "big differences" remain between North Korea and the United States over Pyongyang's nuclear ambitions, but he asserted that the reclusive nation will pledge not to test or transfer nuclear weapons and would ultimately dismantle its nuclear programs if the United States dropped its "hostile policy."

Participants in the event said they could not recall any previous visit by a North Korean official to Capitol Hill. In fact, the Bush administration had previously refused at least twice to permit the official -- Pak Gil Yon, North Korea's ambassador to the United Nations -- to travel to Washington, said Rep. Curt Weldon (R-Pa.). Democratic presidential candidate John F. Kerry has criticized the administration for declining to meet directly with North Korean officials to resolve the impasse.

The State Department must approve any travel by Pak or his deputy, Han Song Ryol, outside a 25-mile radius of new York City. Han made an undislosed visit to Washington in September 2002.

Yesterday, however, Pak and Han spent hours on Capitol Hill, attending an all-day seminar in the Dirksen Senate Office Building with congressional officials, South Korean parliamentarians and Korean experts and holding a news conference. He said he would not speculate on why the administration finally permitted him to visit Washington and said Pyongyang -- which has broadcast pro-Kerry statements -- has no favorite in the presidential race. "It's entirely a U.S. internal affair," he told reporters.

Donald P. Gregg, chairman of the Korea Society, which helped organize the seminar, called the meeting a "historic session" and said it indicated that progress on restarting a dialogue was being made after three years of stalemate.

Sen. Joseph R. Biden Jr. (Del.), senior Democrat on the Senate Foreign Relations Committee, said the administration's decision to permit Pak's travel was "some small measure of the realization on their part that there needs to be this direct contact between us." Earlier this month, Secretary of State Colin L. Powell met with his North Korean counterpart in Jakarta, Indonesia -- the highest-level meeting since North Korea abandoned an agreement to freeze its nuclear programs and began producing weapons-grade plutonium nearly two years ago.

Pak, in remarks to the seminar, reiterated that North Korea believes that the root cause of the standoff is the administration's "hostile policy" toward North Korea. He said Pyongyang "will give up its nuclear program if conditions are met through ending the USA's hostile policy against it." He added that "mistrust and misunderstandings are the biggest obstacles" between the two countries.

Pak said the more detailed proposal advanced by the administration during the round of six-nation talks last month in Beijing had positive aspects, including the administration's willingness to soften the diplomatic language outlining its demands. "However, we also found a lot of regrettable elements in it," he said. "We concluded it was a roadmap to disarm [North Korea] step by step."

Under the U.S. proposal, once North Korea declares it would end its programs, U.S. allies such as South Korea could provide immediate energy assistance. North Korea then would have three months to disclose its programs and have its claims verified by U.S. intelligence. After that, the United States would join in providing Pyongyang with written security assurances and participate in a process that could ultimately result in the normalization of relations.

Pak noted that a state of war still exists between the United States and North Korea and thus the administration's demand that North Korea give up its weapons first before discussions can proceed on other aspects of the relationship "has no credibility in terms of laws or lawyers."

Pak also asserted that the three-month time frame for verifying North Korean claims did not meet favor with other participants at the talks. "The three months of preparation for dismantling the nuclear program has little scientific and realistic nature with no parties' support," he said.

Last week, Chinese Embassy spokesman Sun Weide said at a news conference that China, along with other participants in the North Korean talks, believes the United States must reward North Korea with "corresponding measures" at the moment Pyongyang declares it has frozen its nuclear activities.

Speaking with reporters, Pak again denied U.S. allegations that North Korea has a program to produce highly enriched uranium. He called the charge "totally fabricated." U.S. officials have said that disclosure of the uranium program is essential to ending the impasse.

South Korean officials attending the seminar told Pak that the nuclear issue was an impediment to a better relationship between the two countries. But Pak responded that the nuclear issue was between the United States and North Korea, and should have little bearing on North-South relations.