The People's Republic of China may have shipped nuclear warheads to Saudi Arabia since the Iraqi invasion of Kuwait on Aug. 2, according to highly sensitive intelligence reports given to President Bush.

The warheads would be placed on CSS-2 intermediate-range ballistic missiles the Saudis bought from China, equipped with conventional warheads, in 1985. When the United States discovered the missile sale three years later, China and Saudi Arabia promised the missiles would never be fitted with nuclear warheads.But U.S. intelligence officials now fear that promise may have been broken. Intelligence reports note that the evidence is not conclusive, but that it was serious enough to be included in the President's Daily Briefing. Only several dozen top administration officials see that document, which is used to brief the president on the most urgent intelligence matters. The material in the briefing is classified higher than "Top Secret."

The reports on the alleged transfer say highly reliable sources used by the Central Intelligence Agency implicate the Saudi ambassador to the United States in the deal. The sources say Saudi Prince Bandar bin Sultan asked the Chinese on Aug. 3, the day after the invasion, to give Saudi Arabia chemical and nuclear warheads for the CSS-2 missiles.

U.S. electronic intelligence has detected that the CSS-2s have been in a state of high readiness since Aug. 3.

Prince Bandar negotiated the original purchase of the CSS-2s on a trip to Beijing in 1985. The Saudis were so cagey that U.S. intelligence did not find out about the sale until January 1988. Saudi King Fahd then wrote to President Reagan saying there were no nuclear warheads on the CSS-2s and Saudi Arabia was not looking for any. The recent top-secret reports on the CSS-2s, relying heavily on information developed by the Defense Intelligence Agency, say there has been an influx of Chinese nuclear missile technicians into Saudi Arabia since early August. To mask the buildup, the Chinese reportedly take secret flights to Pakistan and then to Saudi Arabia.

The U.S. intelligence reports maintain that if there are nuclear warheads in Saudi Arabia, the Chinese have insisted on controlling them. One top-secret DIA report says there may be as many as 1,000 Chinese military advisers in Saudi Arabia.

The same DIA report says there are about 50 CSS-2s at fixed and mobile sites in Saudi Arabia. The Saudis originally made a dozen or more of the missiles mobile so they could be hidden from U.S. and Israeli intelligence.

The CSS-2 has a maximum range of 1,678 miles. It is not considered highly accurate and would normally be used against large targets such as cities instead of hardened military targets where the strike would have to be precise.

The Chinese built the CSS-2 for use against the Soviet Union, other Asian countries and U.S. bases in the western Pacific Ocean. But they aren't above selling it, too. China is a major supplier of arms to the Third World, and the Saudis are good customers. In the past eight years, Saudi Arabia has been the largest Third-World arms buyer, followed by Iraq.