A regional council, under pressure from local residents concerned about the effects of radiation, declared a ban on nuclear tests at the Soviet Union's primary test site.

The action came Monday as the international environmental group Greenpeace charged that the Soviet Union has had a nuclear device in an underground shaft on the Arctic island of Novaya Zemlya since December in anticipation of testing there.It was unclear what effect the ban by the Semipalatinsk council in the republic of Kazakhstan, about 2,000 miles southeast of Moscow, would have on the national government's test program, but Moscow has been considering closing its prime test site for years.

Hundreds of nuclear tests have been conducted during the past 40 years at the Semipalatinsk test range, mostly underground but with some in the air.

There has been increasing pressure by local residents on the Soviet government to close the test range. The number of tests has declined in recent years during temporary unilateral test bans and plans made to open a new test site.

The official Tass news agency, reporting the decision of the Semipalatinsk regional council in a two-paragraph dispatch, said the tests at Semipalatinsk had subjected more than 500,000 people to "the harmful effects of radiation."

Greenpeace said in a telex from a delegation visiting the northern Soviet port of Arkangelsk that a ship carrying environmental activists would sail to Novaya Zemlya on Tuesday in an effort to ensure that a nuclear test is not conducted there.

Greenpeace did not say how it had confirmed that the Soviet Union was planning a nuclear test at Novaya Zemlya.

"We have learned that it (the test) has been postponed several times in the last year," Greenpeace coordinator Steve Shallhorn said in the telex. "Our ship will be sailing to Novaya Zemlya in the hope of stopping nuclear testing forever."