What was going on when I was born?

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.

After five years of guerrilla warfare, El Salvador is now hovering in precarious uncertainty, its people worried about a divisive election campaign, unsure about future United States aid and weary of the destruction wrought by the civil war. That is the opinion offered by Salvadoran politicians, some senior Salvadoran military officers, United States Embassy officials and other Westerners here. ''The feeling here is the same as in the States - fatigue with the war,'' said Jose Napoleon Duarte, the Christian Democratic Party's candidate for president in elections scheduled for March 25. Discouragement on Both Sides ''I was in the eastern part of the country recently and a young army commander asked me, 'Senor Duarte, how long do you think this war is going to last? One year? Three years?' I told him, 'At least three years.' He shook his head and said, 'I feel it's too much.' ''

The Gulf Oil Corporation, bracing for a takeover bid by T. Boone Pickens, warned yesterday that if the Mesa Petroleum Company chairman ever got 51 percent of Gulf's shares the company might use $6 billion in bank credits to buy the rest, turning itself into a financial cripple. While the tactic appeared to be one of last resort and intended to affect only Mr. Pickens and his partners, it was viewed as a sign that Gulf might take very drastic steps to fight off an unwanted takeover. Gulf announced last Friday that it had uncovered a plan by an investor group headed by Mr. Pickens to offer cash for enough shares to gain control of Gulf and then pay ''securities of questionable value'' for the rest. Gulf later sued the group in Federal District Court in Delaware, accusing it of market manipulation.

The Soviet Union passed a third day today since the death of Yuri V. Andropov without announcing a successor, but there were growing indications that the Central Committee would name a new leader on Monday. The reasons for not yet naming a leader remained obscure. Mr. Andropov's appointment as General Secretary of the Communist Party 15 months ago was announced the day after Leonid I. Brezhnev's death was formally disclosed, and the break with this limited precedent suggested that the 12 voting members of the Politburo had been unable to reach a quick consensus. Party rules empower the full Central Committee, with about 300 members, to elect a General Secretary. But if the Politburo agrees on a candidate, unanimous approval by the full Central Committee is considered automatic.

''I'm sure that President Reagan is fully committed to help Lebanon recover its sovereignty and independence.

In scarcely a year, the Lotus Development Corporation has done for the world of personal computer software what International Business Machines has done for personal computers: It has created a product so wildly successful that scores of other companies are scrambling to imitate it or improve on it. The company's sole computer program, Lotus 1-2-3, is an ''office productivity'' tool that quickly seized the position last year as the hottest-selling software package in the country. In its first full year of operation, Lotus earned $14.3 million on sales of $53 million, primarily because about two-thirds of all United States companies buying business microcomputers last year chose 1-2-3 for making complex financial projections and displaying the results instantly in computer-generated pie charts, bar charts and other graphic displays. Despite the company's prospects - analysts have been consistently enthusiastic about Lotus since the company went public four months ago - no manufacturer of personal computer software has ever managed to market two runaway hits in a row. For Lotus, poised at the edge of what many expect is an imminent shakeout in the software market, producing that second product is considered crucial if it is to maintain the momentum generated by 1-2-3.

Many of Wall Street's top analysts, trying to explain the stock market's steep decline, have pointed to fears of an economic downturn. But some of those on the front line, who make or arrange transactions involving millions of shares, say that fears of climbing interest rates and growing Federal deficits have only been the spark that ignited the selling streak. These traders say that sheer panic by some institutions was an important reason for the three-week fall of 98.41 points in the Dow Jones industrial average, which closed at 1,160.70 Friday. And once the market fell sharply, the result was mutual fund redemptions and margin calls that pushed prices even lower, the traders said.

They build windmills. They tap natural steam from below the earth's surface. They even burn walnut shells. While electric utilities in most parts of the country continue to plan in terms of either nuclear or coal, some on the West Coast appear to have a better idea.