South African authorities confirmed today that about 65 U.S. citizens are working as nuclear specialists at the Koeberg atomic power station near Cape Town but said the men had cleared with the U.S. Embassy here that they were not violating U.S. law.

However, an embassy spokesman indicated later that the contact had stopped short of giving legal clearance, saying the embassy was merely informing the Americans of the laws affecting their employment in South Africa.

U.S. law requires authorization from the secretary of energy before any U.S. citizen "directly or indirectly" helps certain nations, including South Africa, produce plutonium, which can be used to make nuclear weapons.

Plutonium is a byproduct of the Koeberg plant's reactor, which began operating last year and is now generating between 4 and 5 percent of South Africa's total electricity needs. A second reactor, which will double the output, goes into service later this year.

The Washington Post reported Jan. 20 that South Africa's state-run Electricity Supply Commission (Escom) was suspected of offering high salaries and other benefits to recruit as many as 40 skilled American atomic reactor operators, who may be working at the Koeberg plant in violation of a 1983 law that carries a maximum penalty of 10 years in prison and a $10,000 fine.

Last Wednesday, Energy and State department officials told several members of Congress and congressional aides that 38 unauthorized American workers had been confirmed as working for Escom, according to a source who attended the briefing. U.S. officials say they are attempting to identify the Americans and their duties before deciding what action, if any, should be taken against them.

Andre van Heerden, regional information officer for Escom, which operates the Westinghouse-designed, French-built plant on the Atlantic Coast about 20 miles north of Cape Town, told foreign correspondents today that about 20 Americans were directly employed by the commission as health physicists, emergency planners and reactor operators.

About 40 to 45 others were employed at the plant by U.S. companies contracted by the South African commission to do maintenance and safety work at the power station, van Heerden said.

Van Heerden said Americans had been working at Koeberg since 1976, mostly on three-year contracts. They had helped train South African staff and had been used particularly on quality control.

Van Heerden denied a report that the Americans had been lured to work in South Africa with $100,000-a-year, tax-free salaries plus free houses and cars.