Using a wide variety of carefully crafted ruses, Saudi Arabia successfully hid from U.S. intelligence agencies for more than two years its acquiring of Chinese ballistic missiles with a range of more than 1,000 miles, according to an informed diplomatic source.

The fact that Saudi Arabia, which has such close military and security ties with the United States, was able to carry out this deception suggests a significant failure of U.S. intelligence.

No evidence about the Saudi acquisition of surface-to-surface missiles, or construction of their sites, was picked up before last fall, according to congressional sources. But U.S. intelligence concluded that the Saudis were indeed obtaining the missiles less than two months ago, according to several sources.

"There was a deliberate and extensive effort to hide it," said one congressional source.

The informed diplomatic source said China agreed in principle to sell the missiles in July 1985 when Prince Bandar bin Sultan, the Saudi ambassador to Washington, negotiated the deal in Beijing. The first missiles reached Saudi Arabia late last year, the source added.

The United States did not directly confront the Saudi government with satellite evidence of the 66-foot-long missiles and their sites until March 6, when Assistant Secretary of State Richard W. Murphy met with Prince Bandar at his home here and demanded to know whether Riyadh had obtained "nuclear" missiles from China, the source said.

The administration was alarmed by the evidence because the Chinese missile, which the Chinese call the DF3A and the U.S. intelligence community the CSS2-class, had heretofore been used by the Chinese only to carry nuclear warheads. It had never before been exported.

Bandar reportedly confirmed that Saudi Arabia had obtained the weapons but categorically denied the kingdom had obtained, or ever sought, nuclear warheads from the Chinese. He told Murphy that the Chinese had modified the missile especially for the Saudis to carry a large conventional warhead, a change that reduced the missile's range.

This particular version of the Chinese missile normally travels about 1,600 miles. The exact range of the modified Chinese missile the Saudis have bought could not be learned, but it is somewhat less than that.

Having been taken by surprise by Saudi acquisition of the missiles, the Reagan administration now fears that Israel may carry out a preemptive strike against them that would complicate Saudi-U.S. relations and destroy any chance for Arab acceptance of the new U.S. Middle East peace initiative.

The Saudi decision to turn to China marks a major turning point in the traditionally close U.S.-Saudi military and security relations, including the sharing of much intelligence information.

The Saudis have refused U.S. requests to inspect the missiles to verify firsthand that they do not carry nuclear warheads, telling the Americans this is a question of strict confidentiality between Saudi Arabia and China and reminding them that it does not allow the Chinese to inspect U.S.-provided AWACS surveillance aircraft.

Saudi diplomats, who have been briefing members of Congress on their newly acquired Chinese missiles, have emphasized that Riyadh turned to Beijing for help only after Congress repeatedly rebuffed its efforts to obtain U.S. arms, including F15Es and the short-range Lance missile, which has a range of about 70 miles.

"They felt naked. They did come to us. They asked us for . . . the Lance missile and we were not prepared to sell so they went elsewhere," Murphy told a House committee last Thursday. "I regret it."

Murphy said there had been "grave concern" in the administration that the Chinese missiles carried nuclear warheads, but said both China and Saudi Arabia have provided assurances that this was not so. Bandar has delivered a March 12 letter from King Fahd to President Reagan conveying the assurance in writing.

The Saudis went to great lengths to deceive Washington about their purchase of missiles from the Chinese, according to one knowledgeable source. According to the source, the Saudis have taken the position that they never lied outright to the Americans, but also never told them the whole truth.

The Saudis used a budding economic relationship with China, specifically in the petrochemical field where the kingdom was in search of markets for expanding Saudi production, to develop secret contacts with the Chinese. (Saudi Arabia has diplomatic relations with Taiwan, and does not formally recognize China.)

Bandar's visit to China was made under the pretext that he was trying to persuade it to stop selling arms to Iran. The Saudis told the Americans they had "offered" to compensate the Chinese for the loss of arms sales to Iran by buying the same weapons, including Silkworm missiles, for Iraq. The Saudis also "offered" to have the Iraq-bound missiles from China pass through Saudi territory to assure their security from Iranian attack.

The Chinese then shipped the missiles destined for Saudi Arabia together with those being transshipped through the kingdom to Iraq. After both sets of missiles were counted leaving Saudi ports, those destined for the kingdom were trucked south into the great Saudi desert known as the Rub el-Khali, or Empty Quarter.

There, the Saudis told the Americans they were building a huge "ammunition depot" that they wanted to keep for security reasons far from their cities and populated areas. In fact, the depot was a training and storage area for the Chinese missiles.

The source said the Saudi cover was finally blown in January when the Americans discovered that trucks carrying some of the presumed Iraq-bound missiles were traveling south, rather than north, from Saudi ports.