Even if President Bill Clinton chooses not to proceed with national missile defense (NMD) -- a decision he will make later this year -- the United States will be forced to respond to emerging missile threats at some point, the official said.

Intercontinental ballistic missile (ICBM) dangers from so-called "rogue states" -- including North Korea in the short- to medium-term and Iran in the longer term -- are real and no amount of protest from China, Russia or others will change that, he said.

"I would project that this issue isn't going to go away," the official, speaking on condition of anonymity, told reporters, stressing that US lobbying of Russia to modify the 1972 Anti-Ballistic Missile treaty to allow for NMD would only intensify.

"We are proceeding on the basis of the threat assessments that the intelligence community has laid out and developing a program that has been fleshed out in some detail that would respond to the North Korean capability at the earliest possible date."

"There is a broad consensus in the United States across the political spectrum that the United States needs to respond to this emerging new kind of ICBM threat ...

"And I think it will be important under any administration to update the ABM treaty to make sure that it not only preserves its original purposes but accounts for changes in the international environment that weren't contemplated when the treaty was negotiated nearly 30 years ago."

Clinton is to travel to Moscow next month and the top item on his agenda will be trying to convince his Russian counterpart, Vladimir Putin, and skeptical law and policy makers there that revising the ABM treaty is the only practical course to take in the new atmosphere.

The treaty, signed by the United States and the former Soviet Union and aimed at preserving deterrence as the chief method of avoiding nuclear war by limiting defenses, forbids large-scale systems capable of shooting down incoming missiles.

Russia is opposed to amending the pact, seeing NMD as a direct threat to its security and has rejected suggested modifications submitted to it earlier this year by US officials.

And a top Chinese official has warned that NMD deployment could force Beijing to strengthen its nuclear force as well as develop its own counter measures, creating a new wave of strategic weapons proliferation.

But the US official said Russian fears were misplaced, noting Washington's willingness to accede to a variety of confidence-building measures.

He hinted that even without ABM amendments, NMD could go ahead if the treaty were scrapped as some conservative US lawmakers have suggested.

"What we're trying to do is avoid putting the president in a position where he has to choose between (NMD) that he may well conclude is necessary for the defense of the country and the ABM treaty," the official said.

Chinese opposition to NMD is equally misplaced, the official, stressing that China was not targeted by it and maintaining that Beijing's warning about the system forcing nuclear proliferation was not valid.

"The likelihood is that whether or not we proceed with NMD that China's nuclear forces would expand in a way that could make this system less threatening to China," the official said.

In an interview published by the New York Times Thursday, China's top arms negotiator, Sha Zukang, said deployment of NMD would be countered by Beijing.

"We'll have to do something," he told the paper.

"How can we base our own national security on your assurances of good will?"

He said the proposed anti-missile shield would upset the "balance of terror" that has kept nuclear peace up to now, and would touch off a global arms race and possibly a "nightmare scenario" of weapons proliferation.