The National Academy of Sciences has cancelled workshops, seminars and symposiums with the Soviet Union for at least six months in protest of the banishment of Nobel Laureate Andrei Sakharov.

The move by the National Research Council, ruling body of the academy, was the first taken against the Soviet Academy of Sciences since the two groups began formal exchange 21 years ago.

The news came as, separately, the Carter administration banned "for an indefinite period" exports of phosphates to the Soviet Union [Details on Page D7.]

In a cable to A. P. Aleksandrov, president of the Soviet academy, the academy strongly hinted it will not resume exchanges until the Soviets allow Sakharov to return to Moscow from Gorki, a city 250 miles east of Moscow that is closed to foreigners.

"The council of this academy asks that your accademy convey to the authorities of the government of the U.S.S.R., our profound hope that the safety and freedom of movement of Academician Sakharov and his family will be protected," the cable said.

Sources who attended the closed meeting of the council that ran almost all day Sunday said it was clear from remarks of members that the future of formal scientific exchange with the Soviets hangs on how Sakharov is treated.

One source said, "We want to see him regain his freedom and return to Moscow."

The council's action came before the Soviet Academy meets March 4 in Moscow where, it is widely believed, there will be a move to strip Sakharov of his membership in the academy.

"It's hard to break up something we've all worked more than 20 years to build up," one U.S. academy member said of the council's move, "but there is a very real fear that the Soviet political leadership has not finished with Sakharov."

At the same time, directors of the Institute of Electrical and Electronics Engineers, the world's largest engineering society, said they would suspend their exchange program with the Popov Society, the Soviet counterpart. Like the academy exchanges, the program started in 1959.

The IEEE's program with a delegation from the Popov Society that had been scheduled for May 13-15 in Boston was called off and a planned trip of a 10-member delegation to Moscow later in May was also canceled.

The National Research Council policy-setting arm of the academy, voted 10 to 3 Sunday to cancel four bilateral meetings scheduled in the United States during the next two months.

The first one was to have been a major session on lasers March 3-20 at the University of Arizona in Tucson involving 15 physicists from the Soviet Union and 20 from the United States.

Also called off were three planning meetings between three or four scientists from each side concerning basic research, physics and experimental psychology.

Academy sources stressed that the vote did not mean there were three council members against sanctions. One source said at least one of the dissenting members wanted a year's suspension. Another source said they wanted language in the cable calling a halt to all new exchanges.

A leading Soviet dissident and outspoken foe of nuclear weapons for years, Sakharov is regarded as a hero by many American scientists. Winner of the Nobel Peace Prize in 1975, Sakharov is also a three-time winner of the Order of Lenin and at the age of 32 was the youngest Russian ever elected to the Soviet Academy of Sciences.

In 1973, the National Academy made Sakharov a foreign fellow, a rare move that was triggered by rumors Sakharov was about to be arrested. NAS President Phillip Handler warned the Soviet Union that Sakharov's arrest would result in grave consequences for the Soviet-American exchange program.

Sakharov was seized on a Moscow street Jan. 22, stripped of state honors and sent with his wife to Gorki. He and his wife are said to share an apartment with a woman believed to be a KGB police agent, who monitors his movements.

The academy action Sunday came after a speech by Columbia University mathematician Lippman Bers, a friend of Sakharov for years.

"What I said was that Sakharov has spoken out and now it is time for us to speak out for Sakharov," Bers said by telephone from New York. "I feel that now when he is trouble, we cannot let him down. In our protest, we are doing what Sakharov wants us to do."