What was going on when I was born?

International The first cut in OPEC oil prices in the organization's 23-year history was agreed upon by its 13 members in hopes of regaining control over the world petroleum market. The key cut is a 15 percent reduction - to $29 a barrel, from $34 - in the price of Saudi Light crude and production quotas for all OPEC members except Saudi Arabia. (Page A1, Column 6.) President Reagan stressed to Israel the ''urgency'' of its agreeing on terms for a withdrawal of all its forces from Lebanon, according to an Administration official. Mr. Reagan made the statement to Foreign Minister Yitzhak Shamir, who also met with Secretary of State George P. Shultz for five hours. (A1:3.)

An article about Lever Brothers in Business Day on Saturday incorrectly reported the ownership of a soap called Monchel. It is a Procter & Gamble product.

When critics say the Reagan Administration may have underestimated the cost of its long-range military spending plan, Defense Secretary Caspar W. Weinberger argues that the Pentagon has shed the bad habits that push up the cost of developing and buying weapons. Two years ago the newly installed Reagan team at the Defense Department approved a list of 32 measures to improve the costly and lengthy military procurement system. But there is disagreement and uncertainty about how well the department has succeeded in carrying out its ''acquisition improvement program.'' The argument is important in both practical and political terms. Some members of Congress want to see the long-range spending plan ''repriced.'' If a recalculation showed that future costs had been underestimated, the Administration would either have to scale back its ambitious plan to ''rearm America'' or ask Congress for even larger sums.

American Airlines, in a sweeping attempt to simplify fares, announced a plan yesterday to replace thousands of different fares with four basic ones tied to the distance traveled. Expressing the hope that the rest of the industry would follow suit, Thomas G. Plaskett, senior vice president for marketing, said: ''The new streamlined fare structure will help reduce fare confusion and make airline ticket prices more equitable for everyone.'' Two major carriers, Trans World and United, reacted favorably to the plan. But other airlines were doubtful that the new system would be supported in highly competitive markets.

BROWN chunk of rock, a meteorite found on the ice of Antarctica four years ago, has sent a shock wave of excitement through the laboratories of planetary science. Its drab appearance belies its apparently exotic provenance. The rock very likely comes from Mars. If scientists are right about this, and the evidence is becoming more and more persuasive, the meteorite would assume an importance in the history of science comparable to that of the first Moon rocks returned by the Apollo astronauts. It would be the first known object from another planet to reach the Earth. It would afford scientists their first chance to study in detail the chemistry and geology of Mars. Tests on pieces of the meteorite have recently erased most uncertainty about its Martian origin. After an analysis of gases trapped in the meteorite, Dr. Robert O. Pepin, a University of Minnesota physicist, emerged from his laboratory last week and exclaimed: ''It's from Mars. I don't think there's any doubt.''

The nation's retailers are sure that an economic recovery will bring more shoppers into their stores. But they are less sanguine about whether those customers will buy anything. The problem is service. Although retailers do not have hard numbers, many of them said that more and more shoppers were stalking out of stores empty handed because of trouble with sales personnel. ''The biggest problem in retailing today are the salespeople,'' said Sanford W. Felberbaum, a consultant and former vice president for both Macy's New York and the Bamberger stores. ''They are nonexistent in reality or in their desire to serve customers.''

In June 1981, John Brademas became the 13th president of New York University. Since then Mr. Brademas, a former United States Representative from Indiana and majority whip in the House, has taken steps to develop new academic leadership, expand student financial aid and strengthen offerings in the arts and sciences; last week, the university announced the launching of a $100 million capital fund drive. Mr. Brademas recently discussed his 20 months at N.Y.U. with Edward B. Fiske, education editor of The Times. Following are excerpts from that interview. Q. There's going to be a 40 percent drop in the number of 18-yearolds in this area. What does that mean for N.Y.U.? A. It means, I think, that we must continue to improve the quality of the education that we offer if we're to be able to keep attracting outstanding young men and women. If you look at the application figures for the fall of 1983, we're holding up very well. In fact, there is an increase of approximately 5 percent above the figure from one year ago. Q. A number of colleges are planning to reduce their size as a way of maintaining their academic quality. Smith College, for example, is going to take 10 percent fewer freshmen this fall. Are you thinking in these terms?

The Walter E. Heller International Corporation announced yesterday that it had ended its agreement to sell its two commercial lending units to the Security Pacific Corporation of California and that it had agreed to sell them instead to the Fuji Bank of Japan for a higher price. Fuji agreed to pay $425 million for the two Heller units - Walter E. Heller & Company and the Walter E. Heller Overseas Corporation - compared with Security Pacific's bid of $400 million plus an undetermined portion of future earnings. The Heller companies lend primarily to medium-size companies throughout the United States. Currently the largest independent commercial finance company in the United States, Heller will now be left with only the American National Bank of Chicago, the fifth-largest bank in Chicago, with $3.3 billion in assets.

President Reagan emphasized to Foreign Minister Yitzhak Shamir today the ''necessity and urgency'' of Israel's agreeing on terms for the withdrawal of all its troops from Lebanon as the first step in the complete pullback of foreign forces from that country, an Administration official said. As talks on ending the deadlock in Israeli-Lebanese negotiations intensified, Secretary of State George P. Shultz, in morning and late afternoon meetings with Mr. Shamir totaling five hours, put forth American suggestions on bridging the differences between the Israelis and the Lebanese that have held up an accord for the last 10 weeks. Israeli Security Discussed According to participants in the talks, the United States discussed ways of meeting Israel's security concerns in southern Lebanon by use of international peacekeeping troops, possibly augmented by an increase in American forces. Mr. Shamir has insisted on the principle of having some Israeli military presence in southern Lebanon after the withdrawal of his country's 30,000 troops, to insure that Palestinian guerrillas do not infiltrate into the south.

City officials called a halt yesterday to work on five ''sliver'' buildings -tall, narrow apartment houses that tower over their residential neighbors. The five, which were among 27 existing applications, were stopped because their foundations had not been put in before a ban was imposed on such buildings. Work is proceeding on six others. The status of the 16 remaining projects is uncertain.

The OPEC nations agreed on a price cut for the first time ever. The new accord calls for a cut of 15 percent, to $29 a barrel, in Saudi Light crude, the key to OPEC's price structure. It also lowers the group's production quota to 17.5 million barrels a day, down a million, for the rest of the year. The first test of the pact is likely to come over Britain's North Sea prices. (Page A1.) Mexico cut its prices, too. (D23.) Under the accord, analysts say, Saudi Arabia has lost much of its once-crucial flexibility. (D22.) The new accord may not have gone far enough to keep OPEC from having to cut prices again within six months, according to American oil executives and industry analysts. It will work, they said, only if there is a sharp increase in demand for OPEC oil. They foresaw little or no impact on consumer prices in the U.S. (D22.)

The staff of a Senate subcommittee has found that the use of offshore banks and other facilities has become so pervasive that it ''undermines the integrity of American banks'' and defies the ability of United States law enforcement authorities to enforce the laws. The staff of the Senate Permanent Subcommittee on Investigations, in a study to be released at hearings on Tuesday, also says that the unregulated nature of offshore havens, where most international lending and Euromarket activity take place, creates an environment for criminal activities. The criminal use of offshore facilities, the staff found, may pose as great a threat to the stability of the world's banking system as do questionable loans, poor controls and the inability of debtor nations to pay their debts. 'Backbreaking Straw' ''It is not inconceivable that it could be a criminally derived loss, not the failure of repayment of a loan from a sovereign nation, which could be the backbreaking straw to the banking system,'' the study says.