A prominent Soviet nuclear scientist said yesterday that there is no problem with radioactivity in milk being sold in Moscow, despite a warning from the American Embassy in Moscow that pregnant women and infants in the Soviet Union should not drink Soviet milk.

The American Embassy on Saturday said pregnant American women and infants should avoid drinking Soviet milk because the level of the radioactive element Iodine-131 had increased tenfold in milk since the time of the Chernobyl accident. The embassy said, however, that the radioactivity had not yet reached a dangerous level.

Dr. Yevgeny Velikhov, vice president of the Soviet Academy of Sciences, interviewed on NBC's "Meet the Press," said he had drunk milk that morning, "and in my knowledge there is no problem with milk in Moscow."

He added that there is a region of the Soviet Union where high levels of iodine have been reported, and milk from there is forbidden to be sold.

The Food and Drug Administration, which is testing samples of the milk, said that peak levels of about 3,600 picocuries have been found. Detrimental health effects are not expected to occur at this level, but FDA standards say that milk should not be consumed when it contains more than 8,000 picocuries per quart for adults, or 1,500 picocuries for infants.

Health effects are believed to begin at about the 15,000-picocurie level. The danger of radioactive iodine in milk is that it becomes concentrated in the thyroid. It can cause cancer and, at extreme levels, can shut down the thyroid's function.

Velikhov, who is directing the clean-up of the Chernobyl reactor, also said that a small amount of radioactivity is still being dispersed into the air from the plant. He said a more serious worry is the long-term problem of keeping radioactivity from seeping through the soil into the ground water and from there into the Pripyat River and eventually into the reservoir that provides drinking water in Kiev, a city of 2.3 million.