China announced tonight it had successfully completed tests of at least two intercontinental ballistic missiles into the South Pacific, exhibiting what analysts here see as a significant deterrent to Soviet attack.

The successful launching Sunday of multistaged rockets approximately 6,200 miles to the preannounced South Pacific target reduced the likelihood of a Soviet "surgical trike" aimed at knocking out China's nuclear weapons industry, one analyst said.

"The Chinese may have deployed some of these missiles before the test, and the Russians cannot be sure they could locate them all," he said. If the Chinese were provoked to fire one, he said, "The Russians know now it could de unacceptable damage."

The rockets also are capable of reaching the Western United States.

The Chinese dispatched 18 ships to the splashdown site, a circle with a radius of 70 nautical miles located in the center of a ring formed by the Solomon Islands, Nauru, Kiribati (formerly teh Gilbert Islands), Tuvalu, Western Samoa, Fiji and the New Hebrides.

The Chinese several weeks ago gave advance notice of the upcoming tests and specified the general target area. It was apparently the most distant deployment ever by the Communist Chinese Navy.

In addition to the military importance of the tests, they are seen by Peking as a way to boost its international prestige and rebuild the sometimes faltering pride of the Chinese people in their current government. The official People's Daily, within hours of the first test Sunday, distributed a rare, red-character extra announcing the success and showing a map of the target area.

The official announcement said, "China's launching of carrier rockets into the Pacific Ocean between May 18 and 21 was completely successful." Although it did not say how many rockets were launched, diplomatic sources here said there has been one followup since Sunday's test.

Analysts here have discounted a report from an Eastern European source, hostile to the Chinese missile effort, that one rocket was destroyed in the air Monday when it malfunctioned. Tonight's report congratulated all Chinese scientists and workers connected with the tests.

Analysts say the Chinese had previously proven that they had a missile of intercontinental range, allowing them to hit Moscow and the western United States, when they launched large satellites into orbit.

One analyst suggested that they had then deployed the missiles for retaliation against Soviet attack and saved the first test outside their borders until now, "when they were good and sure it would be a success."

The Chinese announcement did not say what kind of missile was fired. Analysts have suggested it is the CSSX4 (China surface-to-surface experimental No. 4).

The Chinese are thought to have about 40 medium- and 40 intermediate-range missiles, the latter with a range of about 1,750 miles. They also have about 80 old TU16 bombers with a range of 2,000 miles.

Previous CSSX4 missiles have been liquid fueled, but analysts said they assume the Chinese would want to develop a solid-fuel rocket. A recent primer on missiles in a Chinese newspaper hinted they might already have one. The article in the Enlightenment Daily said that in war "time is victory," and liquid fuel took too long to pump into the rocket.

The article, which presented a general description of ICBMs, said such missiles were 65 to 100 feet long, carried an atomic warhead of about one ton and could travel more than 6,000 miles in a half hour.

Chinese rocket testing has been carried out in the Gobi Desert of Xinjiang Province, about 1,000 miles west of Peking. One diplomatic report said, however, that the most recent launchings were from Gansu Province, also in the northwest but somewhat closer to Peking.

The Chinese announcement tonight said there would be no more tests and vessels could safely reenter the target site.

Vice Premier Li Xiannian, traveling in Australia and New Zealand last week, said the missiles would carry no nuclear devices and that China planned no nuclear tests in the Pacific. Chinese newspapers have said the missiles carried measuring devices instead.

Li said in New Zealand that the aim of the tests was to cope with the threat of the hegemonist powers, a Chinese term for the Soviet Union and its allies.