North Korea's demand for a nuclear reactor as a precondition to abandon its nuclear weapons ambitions has dampened the elation that greeted the six-nation agreement signed on Monday.  But the pact was ambiguous on key points, leaving it open to differing interpretations by both sides.

Under the agreement, North Korea agrees to give up any nuclear arms program.  In return, North Korea would get a civilian light water nuclear reactor for power generation. 

But the pact is vague on the timing, saying only that the issue of the reactor would be discussed, as the agreement says, "at the appropriate time." On Tuesday, North Korea said it wants the reactor before it ends its arms program.

As James Lilley, former U.S. Ambassador to South Korea and China, says, North Korea apparently thinks the "appropriate time" is now.

"They signed on to the agreement that said we would discuss the light water reactor at the appropriate time.  Obviously, this was a fudge.  They think the appropriate time is before they dismantle their program.  We think the appropriate time is after they dismantle their program.  This kind of thing is par for the course with them, to come out with some bombastic, extreme statement to increase their leverage and bargaining position," said Mr. Lilley.

The United States reaction to the new wrinkle was muted.  State Department spokesman Sean McCormack said in New York that North Korea should, as he put it, "reflect on the agreement that they signed."

China, which also signed the agreement along with Japan, Russia, South Korea, and the United States, said North Korea was aware of what it signed and called on all parties to implement their commitments in what it termed a "serious manner."  Japan called the new North Korean statement "unacceptable."

Joel Wit, a former State Department senior adviser on North Korea, says the agreement is flawed because it does not lay out any road map of steps for each side to take or a timetable.  Mr. Wit, now a senior fellow at the Center for Strategic and International Studies, says North Korea was bound to try to take advantage of such ambiguity.

"Honestly, I think the agreement, while a step forward, is incredibly vague, and doesn't nail down a lot of important issues," said Mr. Wit.  "So I think the initial reaction to the agreement was really overdone.  I think the administration oversold the agreement.  The press reaction was overdone.  And, in fact, there are enormously important issues that remain to be negotiated."

Mr. Lilley agrees there is more hard bargaining ahead.  But, he adds, just getting the five nations other than North Korea to agree on an approach to North Korean nuclear disarmament was a victory.

"This was an achievement mainly because we got the five countries other than North Korea to agree on something, and to make it public," he added.  "This is a beginning, and this is the North Koreans' worst nightmare, to have the five countries work together.  Because if that happens, they haven't got a chance."

Representatives of the six nations that are party to the agreement are scheduled to meet again in November to work on implementing details of the pact.