The United States and its allies have approved the sale of the most advanced computers ever allowed to go to the Soviet Union, a set of six Control Data Corp. machines that will be used to improve the safety of Soviet nuclear power plants, company officials said yesterday.

The computers will allow the Soviets to upgrade safety standards at more than 50 nuclear power plants; design newer, safer reactors; and better deal with accidents such as the 1986 explosion at Chernobyl. That explosion devastated the surrounding area in the Ukraine and spread radioactive clouds over nearby countries.

"This marks the beginning of a new level of cooperation between the Soviet Union and the United States on issues that affect people worldwide, in this case the safe operation of nuclear power plants," said Jim Ousley, president of Control Data's computer business.

"We are very happy to see that the licenses were approved, given the Soviets' previously negative experience with nuclear safety," said Commerce Undersecretary Dennis Kloske. "It is in everybody's interest to see that they have technology available to them to ensure greater nuclear safety."

The sale is worth $32 million to Control Data, which has been seeking greater access to the Soviet market for years, and it is seen as one of the first commercial reflections of the end of the Cold War and the new spirit of cooperation between Washington and Moscow. Control Data was notified yesterday that the sale had been approved both by the U.S. government and by its allies in the 17-nation Coordinating Committee for Multilateral Export Controls (Cocom), which polices technology sales to the Soviet Union. The first shipment is scheduled for next month.

During his visit to Control Data's Minneapolis headquarters in June, Soviet President Mikhail Gorbachev was shown how the computers could deal with a simulated nuclear plant accident. Jim O'Connell, director of international trade and policy affairs for Control Data, said the computer zeroed in on the location of a burst pipe and gave plant operators instructions on how to first isolate the break and then correct it with a minimum spread of radioactive material.

In addition to approving the sale of the computers, which are six times as powerful as the most advanced computers previously sold to the Soviets, O'Connell said the U.S. government will supply the Soviets with previously restricted nuclear safety software programs.

To gain U.S. and allied approval for the sale, Moscow had to agree to stringent safeguards to prevent the computers from being used by the military. These include giving Control Data workers access to the computers, limiting the kinds of software that can be run on the computers and restricting who can use the equipment. Control Data will monitor the use of the computers.

The safeguards are embodied in a special U.S.-Soviet pact on nuclear safety technical cooperation that was tied to the sale of the six computers.