WASHINGTON (AP) – The chief American negotiator at North Korean nuclear talks said Friday he does not believe Pyongyang is stalling on a pledge to abandon its nuclear weapons, even though three weeks have passed since it missed a crucial deadline.

North Korea has refused to act until it receives $25 million in money previously frozen because of alleged links to money laundering and counterfeiting. American Assistant Secretary of State Hill said the process of getting the North its money has proven extraordinarily complex.

“I know it’s tough to watch the days roll by,” Mr. Hill said. “We think our best interest is in being patient.”

President Bush and other top administration officials have warned repeatedly that American patience is not endless. But Mr. Hill’s comments suggest a willingness to allow Kim Jong Il’s government time to have its money in hand first, which Pyongyang insists is a condition to stopping its nuclear operations.

Mr. Hill told an audience at the Johns Hopkins University school of international studies that North Korea is not using the banking issue to avoid implementation of a nuclear agreement that was considered a breakthrough after a long period of deadlock.

The North missed an April 14 deadline to shutter its main nuclear reactor, which was specified as the first implementation phase of the Feb. 13 disarmament agreement.

American authorities have said the North’s funds are free for withdrawal, but North Korea has yet to take the money. America and North Korea have been in direct contact, Hill said, and the North has expressed its commitment to acting on the agreement once it gets its money.

Despite calls for patience, Mr. Hill’s frustration was evident Friday. He spoke of the “painful banking matter” and said that he would be telling his grandchildren one day about the difficult process.

“It’s been tough,” he said. “Everyone is impatient right now; everyone wants this to get going.”

Meanwhile, North and South Korea agreed Friday to discuss historic trial runs of cross-border railways. The American ambassador to South Korea, however, cautioned Seoul against rushing to embrace Pyongyang before it starts work to dismantle its nuclear program.

Also Friday, American Deputy Undersecretary of Defense for Asian Security Affairs Lawless, said a plan to have South Korea take responsibility by 2012 for commanding its military in wartime would strengthen the American-South Korean alliance.

South Korea, Mr. Lawless said at Johns Hopkins, is eminently capable of defending itself, with American support, in the event of an attack. He said the countries were taking their time to make sure everything goes smoothly in the transition.

South Korea transferred control of its forces to an American-led United Nations command during the Korean War, which was stopped by a truce in 1953. South Korea regained peacetime control of its military in 1994, but America retained control should war break out again.