For the first time in eight years, Soviet military forces have begun maneuvers in the politically-sensitive Kurile Islands north of Japan.

Ignoring a Japanese protest, the Soviets announced target practice would be held off one of the islands and sent a force of landing craft to the area, apparently to practice amphibious assaults.

There were also reports, officially denied here, that Soviet transport planes had landed troops on one island for maneuvers.

The four islands were taken by the Soviets after World War II but are still claimed by Japan, whose repeated requests for the return have been rejected.

Last week, the Soviets announced they had declared waters off Etorofu island, a danger zone for shooting practice from June 5 to 11. Japan protested to Moscow but, according to Foreign Ministry sources, the reply was merely a restatement of Soviet claims on Kuriles Nineteen Japanese fishing vessels were called out of the waters.

It was not clear how large a force is involved. The Japanese Defense Agency confirmed that Soviet landing craft carrying troops were headed for the Kuriles early this week and that some assault meaneuvers were possible.

The Defense Agency denied published reports that Soviet transport planes had landed 1,000 troops on one island. It also disputed reports that the force included cruisers, destroyers and submarines, saying that those ships were part of a routine Soviet naval maneuvers now taking place near Okinawa to the south of Japan.

Soviet maneuvers on the Kurile Islands were common as lat* e as 1970, but none had occurred since. Once the base of a Soviet army division, the islands are now occupied by a small force consisting mainly of coast guard crews keeping watch over fishing grounds.

Japanese officials, while irritated by the maneuvers, were inclined to treat them lightly and showed no sense of alarm. Soviet firing exercises are common in other Russian-controlled areas of the north Pacific, they noted.

There was speculation that the Soviet exercise was intended to put pressure on Japan as it prepares once again to try to negotiate a peace treaty with China. The Soviets have repeatedly denounced that proposed agreement because the Chinese are insisting on a clause opposing the dominance of any one country in Asia. The Russians say this "anti-hegemony clause" would be aimed at them.

Foreign Ministry sources said they had no reason to assume the exercise was a Soviet pressure-play aimed at the negotiations with China.

"There is no reason to think it is intended with any political purposes in mind," said one official. "But I wonder if it is wise on their part to be doing it at all."

News reports saying the exercise included a large navy task force and transport planes received prominent play in Japanese newspapers yesterday, despite official denials.

The Soviet naval buildup in the north Pacific causes the Japanese military establishment great concern and is frequently cited as a reason for building up Japan's army and air force.