The lead U.S. negotiator says the agreement to end North Korea's nuclear weapons program is only a beginning.  Envoy Christopher Hill told a House Committee more steps are necessary to ensure that North Korea dismantles its nuclear program.  His comments Wednesday came a day after two U.S. intelligence officials said they could not verify North Korea's future compliance.


What North Korea has committed to do is to shut down the Yongbyong nuclear plant ? its only known plutonium production facility for nuclear explosives.  The plant also will be sealed and international inspectors given access.  In return, North Korea will receive the first in a series of shipments of fuel oil. 


Envoy Christopher Hill says the agreement requires action within 60 days.  "It establishes tight timelines for actions that are measured in months, not in years, but in months,? he said.


Hill told the House Foreign Affairs Committee it is only a first step.  The agreement signed on February 13 in six nation talks requires Pyongyang eventually to dismantle its nuclear program.  It does not lay out how to deal with North Korea's nuclear weapons, or what some say is a secret plant that produces highly enriched uranium.


Democratic Congressman Howard Berman of California says the stakes are high.  ?The theory I have put forward is they will keep the first dozen nuclear weapons they can build.  I guess they need a 13th to test, they?ve already done that.  And after that the next one goes up for auction on the internet site EBay,? he said.


Congresswoman Ileana Ros-Lehtinen of Florida says negotiators still need a comprehensive solution.  ?This means nothing less than a complete, verifiable and irreversible dismantling of North Korea's unconventional weapons program,? the Republican lawmaker said.


The key word is "verifiable.?  U.S. officials admit it is difficult to know what is happening inside the borders of one of the world's most secretive governments.


In Washington, D.C. Tuesday, intelligence officials told the Senate Armed Services Committee the U.S. might have trouble verifying Pyongyang's compliance.  The officials did say that North Korea appears now to be taking the first steps toward closing down its Yongbyong reactor.  But Lieutenant General Michael Maples, who heads the Defense Intelligence Agency, and the Director of National Intelligence, John McConnell, raised concerns after questions by Senator John Warner of Virginia.


"What does our intelligence show that  the North Koreans will likely carry out this agreement?" asked the Republican senator from Virginia.


"There are parts of this nuclear program that we have to pay a lot attention to see if we have the kind of disclosure and the inspection capabilities that we are looking for,? General Maples said.


McConnell, the new director of national intelligence, says, "We can verify many of the conditions from external observations.  But not at the level you are asking about in terms of details."


Under the agreement, North Korea must destroy all of its hidden nuclear weapons materials.  Hill told Congress that negotiators will require a complete list of declarations.


"But clearly we have to be able to verify this,? Hill said.  ?And I can assure you, what we will not end up with is an agreement where they pretend to disarm and we pretend to believe them."


But Hill did not say how the five other nations later would ensure that North Korea is actually discarding its weapons and dismantling its nuclear production facilities.