Forty-five U.S. experts on China have written to President Clinton urging him to delay his decision on building a national missile defense. They argue that a "precipitous decision" would increase tensions and lead China to accelerate the modernization of its relatively small nuclear arsenal.

"U.S. plans for (national missile defense) are viewed by China as a sign of increased hostility toward their country," they wrote in a letter to the president Thursday.

Russia also strongly opposes the missile defense project, which is designed to protect all 50 U.S. states against attack by long-range missiles. North Korea, Iraq and Iran are cited by the Pentagon as potential threats, although none has yet tested a ballistic missile capable of reaching American territory.

The current plan for a network of missile-tracking radars, anti-missile interceptors and high-speed computers — if deployed as envisioned by the Pentagon — would "adversely affect U.S. relations with China," the China experts wrote. 

Clinton is due to decide this fall whether to give the go-ahead for early construction work that would keep the Pentagon on schedule for eventual deployment of a missile defense system by the end of 2005. More production and legal decisions would be faced by Clinton's successor before the system would be ready for use. 

At a news conference Wednesday, Clinton said he had not made a final decision but intended to do so in the next several weeks. One factor in his decision-making will be the outcome of a test, scheduled for July 7, in which an interceptor missile will be launched from California to attempt to collide with a mock warhead over the Pacific Ocean. In two previous such tests, one succeeded and one failed. 

Clinton said that among other factors he will consider is the likely reaction of the Chinese and other foreign countries. 

In their letter to the president, the 45 private experts said China is likely to respond by modernizing its nuclear weapons. Currently, China has about 18 long-range missiles capable of reaching U.S. territory. Although the Pentagon says the missile defense system it proposes is not intended to negate China's nuclear deterrent, it will be designed to knock down as many as a couple of dozen warheads. 

China "believes that even a simple missile defense configuration will leave its nuclear arsenal vulnerable," the letter said. It urged Clinton to take more time to consider the implications for U.S. foreign relations and to "develop cooperative approaches to curbing missile proliferation." 

The signatories to the letter include Arthur W. Hummel, Jr., a former U.S. ambassador to China, and Paul H.B. Godwin, a retired National War College professor who has had extensive private contacts with Chinese officials in recent years.