WASHINGTON (AP) - A new U.S. intelligence report predicts China would accelerate its nuclear arms buildup if the United States erected a national defense against long-range missiles.

The prediction, in a classified report known as a National Intelligence Estimate, was disclosed Wednesday by U.S. officials speaking on condition of anonymity. They said it is part of a broader assessment of how foreign countries might respond to a U.S. decision to go ahead with a national missile defense.

President Clinton has said he would decide soon whether to authorize the initial steps toward deploying a network of missile interceptors, missile-tracking radars and battle management computers to defend all 50 states against a small-scale nuclear attack. China is among the few nations capable of a nuclear strike on the United States.

In making his decision, Clinton has said he would take into account four main factors: the urgency of the missile threat, the cost of a missile defense, the feasibility of building a reliable defense and the implications for U.S. foreign policy, including responses from China and other nations.

China and Russia are strongly opposed to the U.S. plan, arguing it would undercut the deterrent value of their nuclear arsenals, violate the 1972 Anti-Ballistic Missile Treaty and undermine global stability. As well, many U.S. allies in Europe are leery.

Clinton and his national security aides have tried, with little apparent success, to convince China's leaders that a U.S. national missile defense would not be directed against China's nuclear missile capability. A defensive system, they contend, would be for ``rogue'' nations like North Korea and Iran that are pursuing intercontinental ballistic missile technologies and might not be deterred by U.S. nuclear threats.

Separately, an unclassified CIA report released Wednesday said China increased its missile technology assistance to Pakistan last year and also had a hand in missile development in North Korea, Iran and Libya. The report said, ``The Chinese have taken a very narrow interpretation of their nonproliferation commitment.''

In Islamabad, Pakistani Foreign Minister Abdul Sattar denied that China was aiding his country's missile program.

The spread of missile technology is at the heart of the Clinton administration's justification for developing a missile defense.

The fear is not only of an attack but also of the possibility that a country like Iraq - if armed with a missile capable of striking a U.S. city - might try to use the threat of an attack to persuade the United States to stay out of a regional crisis such as a conflict in the Persian Gulf.

U.S. officials who are familiar with the classified intelligence report said it states that China plans to increase its nuclear arsenal regardless of U.S. national missile defense plans. However, it adds that the increase likely would be sped up if a missile defense were built.

``Would they probably accelerate it? Yes,'' said one official.

Additions to China's nuclear arsenal probably would be modest, the report said, and designed to give China a numerical edge over the U.S. missile defense system, which in its initial configuration might overcome a couple dozen incoming missiles.

The New York Times reported Thursday that the intelligence report estimates that China might increase its arsenal of intercontinental ballistic missiles from the current 20 to as many as 200 by 2015, and that this might prompt India and Pakistan to respond with their own nuclear arms buildups.

The Times also said the report predicts that deployment of a U.S. national missile defense could prompt Russia to resume placing multiple warheads on missiles that now carry only one - a practice Russia agreed to stop as part of the START II nuclear arms reduction pact that it ratified this year.

The CIA said last year that China has about 20 long-range nuclear missiles capable of reaching any part of U.S. territory. It said then that China was likely to test within the next several years a longer range missile capable of being fired from a mobile platform, and that it would be targeted mainly at the United States.

The CIA also has reported that China is developing a submarine-launched nuclear missile, the JL-2, which the intelligence agency said was likely to be tested within the next decade. It said the JL-2 probably will be able to target the United States from waters near China.

The classified report also affirms an intelligence estimate of September 1999 that the United States most likely will face a missile threat by 2015 from North Korea, probably from Iran and possibly from Iraq, the officials said.

The report also predicts that Russia would continue shrinking its nuclear force, which has been eroded in recent years by a lack of money to modernize. Russian officials have warned that they would feel compelled to respond to a U.S. missile defense, possibly by withdrawing from major arms control agreements.

Additions to China's nuclear arsenal probably would be modest, the report said, to give China a numerical edge over the U.S. missile defense system, which in its initial configuration is designed to defeat a couple of dozen incoming missiles.

Anthony Cordesman, a national security expert at the Center for Strategic and International Studies, said in a report last month on likely Chinese reactions to U.S. missile defenses that Washington might be able to negotiate ceilings on China's strategic force in exchange for clear limits to the U.S. defenses.

Cordesman concluded, however, that China was more likely to reject such a negotiation and instead would react to U.S. deployment of missile defenses by ``systematically upgrading its strategic nuclear forces to ensure that it can saturate and defeat any national missile defense system the United States deploys.''