WASHINGTON, Aug 10 (AFP) - The United States could prompt China to multiply its nuclear arsenal by ten times if it deploys a proposed missile defence shield, reports quoting a classified CIA intelligence study said Thursday.

The report, details of which were leaked to leading US newspapers, also warned Russia could conclude the system would render its nuclear arsenal obselete and mount multiple warheads on single tipped missiles.

The assessment appears to bolster arguments by opponents of the National Missile Defence (NMD) scheme, who argue deployment could trigger a new nuclear arms race and trash current arms control treaties.

US officials are adamant however that the land-based system they have in mind would be capable only of repelling limited strikes by adversaries such as North Korea.

Officials familiar with the report also told dailies that North Korea, Iran and Iraq could bring the United States into range of their ballistic missiles by 2015.

The threat from North Korea could be even more imminent, the reports said, bolstering some claims that Pyongyang could hit the United States within five years.

China, the report said, is already modernizing and modestly expanding its arsenal of around 20 intercontinental ballistic missiles, but would probably expand its force to as many as 200 missiles if the US shield is deployed.

Unnamed sources quoted in stories in The New York Times and The Washington Post said that Russia, though unable to bear the cost of a large-scale build-up, would be likely to pack more warheads on exisiting missiles.

The US State Department habitually refuses to comment on intelligence matters, but spokesman Richard Boucher on Thursday made clear once again, that NMD was not envisaged with large scale nuclear powers in mind.

"The system that we're talking about is designed to deal with emerging long-range ballistic missile threats from states of concern. It's not designed to threaten or to undermine the Chinese or Russian nuclear deterrents," he said.

No decision has yet been taken on whether to go ahead with the National Missile Defence System, but the project has already been drawn into election year politics.

Republican presidential nominee George W. Bush has promised to deploy a much more comprehensive system than the land-based limited system envisaged by the Clinton administration.

His plan for a sea and even space based system has promoted accusations that a vital foreign policy decision is being driven by domestic political considerations.

President Bill Clinton has not yet decided whether to go ahead with the system, and is awaiting a recommendation from his Secretary of Defense William Cohen.

The Pentagon however has dropped hints this week that the system might not meet its 2005 deployment goal, citing a string of technical delays ranging from glitches in current anti-missile rockets to designing new projectiles.

Clinton has said he will make his decision on four criteria: potential threat, national security, cost and technological feasability.

Many observers however believe he will delay a decision and leave it up to his successor, who takes office in January.

The CIA report, included in a study known as the National Intelligence Estimate makes no recommendation for or against NMD.

It was sent to Clinton in the last few days and is destined for Congress.

Publication of its contents comes only one day after a separate CIA report accused China of stepping up support for Pakistan's missile program and funelling ballistic materials to US adversaries North Korea, Libya and Iran.

The report also claimed Russian and North Korean firms were implicated in exporting technology crucial to the manufacture of weapons of mass destruction and missile technology.

That alleged proliferation activity is cited by supporters of NMD as a reason why protection against missile attacks is so sorely needed.

Both Pakistan and China strongly rejected the claims of the CIA proliferation report published on Wednesday.

"There is no law in the world which prohibits cooperation between states in the field of defence," said Pakistani Foreign Minister Abdul Sattar.

China meanwhile slammed the accusations as "baseless" and the product of "alterior motives."