February 13, 1984

American scientists say the Japanese have forged ahead in a heated international race for sophisticated supercomputers by creating machines that are more flexible, easier to use and aimed at a wider market than the specialized computers manufactured in the United States. The implications, they say, are that the Japanese advances could mean stiff competition for American makers of large business computers, such as the International Business Machines Corporation. ''What's revolutionary is that these fast Japanese machines could be used by business or government,'' said Dr. Steven A. Orszag, a computer scientist at the Massachusetts Institute of Technology and one of the first American researchers to test the new Japanese machines. ''In the past, the uses of supercomputers have been much more specialized and mainly scientific.'' Supercomputers are the fastest computers of all, working up to 200 times more quickly than large general-purpose business computers. The United States had long held the lead in their manufacture, but Japan in the past few years has been racing to catch up.

A yearlong undercover operation by United States Customs agents has ended with the arrest of five people in New Jersey on charges of conspiring to smuggle more than $1 billion worth of classified high-technology military equipment to China. The Customs Service said yesterday that the five had met with an undercover agent at a restaurant in New Jersey Saturday night and had given him a shopping list of 14 state-of-the-art items, mostly classified, that they wanted to buy. The items, customs officials said, are used in missile guidance, radar jamming and electronic surveillance. ''It was very clear that they were buying on behalf of the Peking Government and that they planned to divert the equipment through Hong Kong to Peking,'' said Patrick T. O'Brien, an assistant commissioner for enforcement with the Customs Service in New York.

Designation of a new Soviet leader is likely today, according to growing indications in Moscow. The delay in announcing a successor to Yuri V. Andropov suggested that the 12 members of the Politburo had been unable to reach a prompt consensus on the new leader. A stalemate in the Politburo would give the Communist Party's Central Committee an opportunity to review the issue. The Committee is expected to meet today. (Page A1, Column 6.) State Department sources believe that the new Soviet leader will be Konstantin U. Chernenko, 72 years old, who was a close associate of Leonid I. Brezhnev. Mr. Chernenko was named Friday to head the funeral commission for Mr. Brezhnev's successor, Yuri V. Andropov. (A7:1.)

IN about three hours, Kitty and Peter Carruthers would be on the ice at the XIV Olympic Winter Games in the pairs' free-skating program. But last night, at a little restaurant in a snow-drifted neighborhood near the Zetra arena, their parents were having dinner and talking about the adopted brother and sister who would win the first medal here, a silver, for the United States team. ''Even when she was little, Kitty could always spin and turn,'' Charley Carruthers remembered. ''She never got dizzy, she never fell.''

As has happened before, the world is learning more about a Soviet leader in death than during his lifeftime. For example, the lying-in-state ceremonies for Yuri V. Andropov, who died Thursday at the age of 69, have revealed that he had a living wife, Tatyana. At the outset of his 15- month tenure in the Kremlin many Western reports described him as a widower. Six weeks ago the United States Embassy here was sufficiently doubtful that it asked the Foreign Ministry whether President Reagan's New Year greetings should be addressed to both the Soviet leader and his wife. Lingering Uncertainty The answer was affirmative, but doubt lingered until the lying-in-state. In the front row of seats reserved for the dead leader's family, her reddish- tinted hair held in place with a hairclip, sat a woman of late middle age identified as Mr. Andropov's widow. Officials supplied her first name.