Rochester Gas & Electric Co. has been granted a license to import $45 million worth of uranium enriched in the Soviet Union, the first time an American electricity company has gone outside the United States to buy uranium to generate nuclear power.

The license was approved last month with the consent of the State Department by the staff of the Nuclear Regulatory Commission, which has the authority to approve uranium imports without the approval of the five members of the full commission. The first shipment of the Soviet-enriched uranium is expected as early as next month.

In confirming and explaining the purchase, a spokesman for Rochester Gas & Electric said it was done for financial reasons. He said the company will save $2 million by purchasing the Soviet-enriched uranium instead of buying it in the United States.

Though the purchase of uranium enriched in the Soviet Union is of no strategic importance, it represents a major breakthrough into a market once monopolized by the United States. For the last 20 years, the American nuclear fuel industry together with the U.S. government so dominated the enriched uranium business that they never even considered any other nation as a competitor.

The import license involves 94,600 pounds of enriched uranium, to be imported by a firm called Separative Work Unit Corp. of Gaithersburg, Md., over a five-year period ending in 1984. The uranium will be used for five refuelings of the 10-year-old Ginna nuclear plant on the shores of Lake Ontario in Ontario, N.Y.

Rochester Gas & Electric explained that it is not importing the fuel directly from the Soviet Union. The company will get the uranium from a company in West Germany, where it has been kept in storage for the last two years.

The uranium is in the form of a gas known as uranium hexafluoride; it was to be fabricated into fuel rods in West Germany and delivered to Austria. Austria contracted to buy the enriched uranium from the Soviet Union, which delivered it to the West German fabrication firm months before a special election killed nuclear power in Austria in 1978.

Since then, Austria has been looking for a buyer so it can cut its losses on the purchase, according to Energy Daily, a newsletter that first reported that an import license had been granted. But before Austia could sell the uranium, it had to win Soviet approval to transfer the material.

Soviet approval of the transfer to Rochester Gas was apparently granted earlier this year, before Nuclear Regulatory Commission approval of the import license. Sources at the State Department and the NRC said that Bonn's approval of the sale was all that was left before the uranium could begin to leave West Germany for the United States.

When the uranium reaches the United States, it will be fabricated into fuel rods by an American company and then shipped to the Ginna plant. The next refueling at Ginna is scheduled for April. The plant is normally refueled once a year when a third of the spent fuel rods are removed and replaced with fresh fuel.

Once Rochester Gas takes possession of the fuel, it will own the fuel even after it becomes spent itself. This means the spent fuel containing plutonium will not be sent back to the Soviet Union the way East Bloc countries do with uranium supplied them by the Soviets.