Three U.S. Air Force F16 fighter-bombers touched down at an air base in northern Japan today, the first of about 50 due to be deployed there to strengthen striking power against the Soviets in northeast Asia.

No U.S. combat jets have been based in northern Japan since 1972. The F16s' arrival, planned 2 1/2 years ago, is depicted by the United States and Japan as a response to a Soviet military buildup in the region.

Twenty-one more of the jets are to arrive at the joint U.S.-Japanese Misawa Air Base on northern Honshu Island by the end of July, to make up one squadron. A second squadron is due in 1987.

The three jets appeared over Misawa in formation with Japanese F1 fighters, as a symbol of close military cooperation between the two countries' armed forces.

Prime Minister Yasuhiro Nakasone, during his two years in office, has worked to tighten military links with the United States and to build up Japan's 180,000-member armed forces. The two countries are also working to improve security over defense of sea lanes around Japan.

The decision to send F16s has been condemned by the Soviet Union as a preparation for war. It has also drawn fire from some Japanese opposition leaders, who argue their country is risking being drawn into a confrontation with the Soviets.

In Misawa, news of the jets' arrival sparked protests from citizen groups, because of political opposition from the Japan Socialist Party and concern over noise.

The F16, one of the most modern jets in the Air Force inventory, has a combat range without refueling of about 600 miles. Although it can function as an air-to-air fighter, its main strength is considered to be ground attack.

From Misawa, the planes would be able to strike a large sector of the eastern Soviet Union, including Vladivostok, Sakhalin Island, the Kurile Islands and a cluster of small islands claimed by Japan that were seized by the Soviets in 1945.

The Soviets have expanded their Far East forces in recent years. According to Japan, about 370,000 Soviet troops and 2,200 combat aircraft are now assigned to the area east of Lake Baikal, although many seem to be directed against China rather than Japan. The Soviets' Pacific fleet has grown to about 825 vessels, according to Japan. About 135 SS20 missiles, many of them presumably targeted on Japan, also have been set up in the region.

Japan says thousands of Soviet troops are stationed on the disputed islands, the closest of which is visible from Japan's Hokkaido Island. On one of the islands, they have based 40 MiG23 fighter-bombers.

Japan now has the world's eighth largest armed forces in terms of budget, ranking after those of France. But operational flexibility remains restricted by the postwar "peace constitution" and active distrust of the military in many sectors of society.

Opposition members of the Diet, or national assembly, scrutinize new weapons systems for any possible offensive applications. Long-range aircraft, with the implied ability to commit aggression and hit the Asian mainland, are especially controversial.

Japan has no aerial refueling tankers, which can extend the range of fighters. Under pressure from the Diet several years ago, refueling nozzles in the noses of Japanese F4 fighters were removed to preclude any possible use with U.S. tankers.

In the 1970s, Japan developed a military jet transport but deliberately gave it a short range due to political considerations. Itnow has to buy U.S. C130 cargo planes for long hauls to Pacific Islands.

The job of flying the F16s is left to the Americans. But Japan is assisting with money, and by building housing and other support facilities at Misawa. About 3,500 more American military personel and their families are being brought to Misawa, which will raise the U.S. population there to about 14,000.