President Bush has offered good advice about the off-again, on-again North Korea nuclear deal. The United States, he said recently, must remain“firm and patient”as President-elect Barack Obama assumes the challenge of separating North Korea from its nuclear program.

We won’t dwell on the fact that if Mr.Bush had followed that course from the start of his administration, North Korea might not be sitting on enough plutonium for six or more nuclear weapons. His prescription was good; the administration still isn’t following it.

Before Mr.Bush spoke, the State Department announced that the United States and its partners would halt deliveries of heavy fuel oil because Pyongyang refused to agree, in writing, on a plan for verifying its nuclear stockpile and facilities.

China and Russia insisted that they had not agreed to any such decision. South Korea said it would delay shipping steel plates for North Korean power stations. Japan was already reneging on its commitment to supply fuel aid, and Australia, which had stepped into the breach, announced that it would withhold its contribution.

If the shipments stop, North Korea would be within its rights to stop disabling its nuclear facilities at Yongbyon and resume producing plutonium for weapons. That would present Mr.Obama with an immediate crisis.

North Korea has a long history of cheating, and robust verification is essential. That includes getting it to commit in writing to allow inspections of key facilities, interviews with scientists and environmental sampling. But under the deal, a verification plan was supposed to come later. The timing was pushed forward as a condition for taking North Korea off the terrorism list by hard-liners seemingly bent on sabotaging the agreement.

The deal is premised on action-for-action, including that Washington and its allies provide one million tons of heavy fuel oil in return for North Korea’s disabling the reactor and fuel production facilities at Yongbyon. By one estimate, Pyongyang has completed 85 percent of the disablement while the United States and its partners have delivered no more than 60 percent of the fuel oil.

North Korea missed an opportunity to set a positive tone with the new Obama administration by not signing a formal verification plan now. Its leaders may want to deprive Mr.Bush of a last-minute foreign policy success or may be hoping to force his successor to offer more fuel or other benefits. They shouldn’t count on it.

As Mr.Bush suggested, Mr.Obama must be firm and patient as he takes on the challenge of persuading Pyongyang to give up its weapons and stop selling nuclear technology and know-how.

He should signal early on that he is sincerely committed to full relations with a nuclear-free Pyongyang and include a North Korean official in a Washington event soon after his inauguration. Mr.Obama also must leave no doubt that he will push the Security Council to impose dormant sanctions - approved after Pyongyang’s 2006 nuclear weapons test - if North Korea walks away from the deal.