What was going on when I was born?

International Robert C. McFarlane is President Reagan's new national security adviser. In making the announcement, Mr. Reagan strongly praised Mr. McFarlane, a retired Marine Corps lieutenant colonel who recently served as the President's special Middle East envoy, in an apparent effort to ally concern about the appointment among Republican conservatives. The appointment, which does not require Senate confirmation, took effect at once. (Page A1, Column 6.) Iran's threats to close a waterway in the Persian Gulf region were assailed by Secretary of State George P. Shultz. It was the first time that Mr. Shultz had suggested that the Reagan Administration might be shifting its policy away from neutrality in the Iran-Iraq war. (A1:3.)

''I only wish the election were really next Tuesday rather than a year from now.'' - Senator Paul Laxalt, Republican of Nevada. (A22:3.)

DETECTION of many fetal defects as early as the 10th week of pregnancy may soon become practicle because of a new technique that some experts expect to replace most uses of amniocentesis, currently the standard test for such conditions, within the next several years. The new method is called chorionic villus biopsy. Unlike amniocentesis, which relies on fetal cells found in samples of amniotic fluid taken with a needle through the abdominal wall, chorionic villus biopsy samples fetal tissue directly through the cervix. It is now being tested at several medical centers in the United States and Europe almost a decade after a primitive version of the technique was first tried in China. A small group of experts will meet today at the National Institute of Child Health and Human Development in Bethesda, Md., to discuss the technique. Experts have high hopes for it, but the method has not yet been used widely enough for its safety and efficacy to be evaluated thoroughly. Dr. George G. Rhoads of the institute said the group would discuss optimum ways of answering these questions.

The long-expected battle to revamp the giant Gulf Oil Corporation of Pittsburgh erupted yesterday with the disclosure by T. Boone Pickens Jr., the Texas oilman, that a multimillionaire group he headed had spent $630 million for 8.75 percent of Gulf's stock and was committed to raising its purchases to $1.1 billion - a stake of nearly 15 percent. The purpose, the group told the Securities and Exchange Commission in a 63-page filing, is to bring about ''a significant appreciation'' in Gulf's market value. Wall Street analysts seemed to place considerable importance on the group's plan to break up Gulf into at least two parts, creating a royalty trust to be given to shareholders. The royalty trust would essentially be a collection of Gulf oilfields spun off into a trust that would permit earnings from the fields to escape many corporate taxes. Units in the trust, similar to shares in a corporation, could be traded on the stock exchange and the earnings of the trust would be paid out in the form of royalty payments to the unit holders.

THE three Nobel Prizes in science and medicine have long been the most prestigious of awards. Each year scientists throughout the world compete desperately for them; universities scramble to hire the winners; nations routinely count them up as measures of scientific prowess, and the Nobel laureates become instant celebrities whose advice is sought on everything from research to war and peace. But criticisms of the awards process are being made by a small band of scholars who have been analyzing Nobel choices and records in an effort to evaluate how well the selection committees have done since the first winners were chosen in 1901. These scholars have concluded in particular that restrictions in the will left by Alfred Nobel, the Swedish industrialist who established the prizes, actually freeze out some of the truly towering figures of science - researchers who by almost any definition are more important than many of those who receive the prizes. The critics find evidence that the committees have been swayed by rivalries and jealousies having little to do with scientific merit. Moreover, there are some who believe that the awards do more harm than good.

By convincing at least four New York couples recently that he was a friend of one of their children, a young man who said he was both a Harvard student and the son of the actor Sidney Poitier gained entrance to their homes, dined with them, borrowed money, stayed overnight and walked out. His unwitting hosts included Osborn Elliott, dean of the Columbia University Graduate School of Journalism, and John Jay Iselin, president of WNET, Channel 13. ''This is a new scam to me,'' said Lieut. Edward Shea of the Police Department's special-fraud squad, ''but we know the kind of people who would try it. They live by their wits. They do it more for the challenge than anything else.'' Mr. Poitier has no son.

CBS is actively seeking to acquire ''one or more major record companies,'' the company announced yesterday. Walter R. Yetnikoff, president of the CBS Records Group, said CBS had been motivated by the proposed merger of Warner Communications' recorded music business and Polygram Records, which is owned by Philips N.V. of the Netherlands and Siemens of West Germany. ''I never thought this sort of thing was legal,'' Mr. Yetnikoff said, adding, ''If it is given legal approval, then we too would like to pursue a course of acquisition.'' It is still unclear, however, whether such mergers are within the bounds of antitrust law. Warner submitted the proposed merger for Government approval last month, and the Department of Justice has not yet responded. The merger has to be approved as well by the West German Government.

The Metropolitan Transportation Authority will need $10 billion more than it is now spending to rebuild the subways and renovate commuter rail lines, the chairman-designate of the M.T.A. said yesterday. An $8.5 billion, five-year reconstruction of the systems that began Jan. 1, 1982, is not sufficient to rejuvenate them, the nominee, Robert R. Kiley, said. He characterized the subways as ''a system in advanced decline.'' ''The $8.5 billion is very important,'' he said, ''but it's by no means the final solution to the problem. We probably need another $10 billion out there.'' He was referring to additional funds from the Federal, state and city governments.

Companies A group led by T. Boone Pickens Jr. has spent $630 million to buy 8.75 percent of Gulf Oil, and plans to raise its purchases to $1.1 billion, giving it nearly a 15 percent stake. The Texas oilman and his colleagues told the S.E.C. their aim is to increase Gulf's market value. (Page D1.) CBS is seeking to acquire ''one or more major record companies,'' according to the company. The move, it said, is in response to a proposed merger of Warner Communications' recorded music business and Polygram Records, which is owned by Philips of the Netherlands and Siemens of West Germany. (D1.)

An exhibition of American agricultural and food- processing equipment, the first American trade show in the Soviet Union since 1977, opened in a Moscow park today with 105 companies displaying everything from giant combines to fast blini makers. Called ''Agribusiness USA-83,'' the exhibit was conceived last November by the U.S.-U.S.S.R. Trade and Economic Council, an organization of American companies and Soviet enterprises, after President Reagan said he would keep agricultural exports free of sanctions and boycotts. Clustered in a 5,500-square-yard pavilion in Moscow's Sokolniki Park, a diverse group of exhibitors that included International Harvester, John Deere, Dow Chemical, Monsanto, Ralston Purina and the state of Nebraska set up their slide shows, samples, snack bars and pamphlets to attract a share of the billions of dollars that Moscow is expected to spend on its crash ''food program.'' The program was started 18 months ago by the late Leonid I. Brezhnev and accelerated by his successor as Soviet leader, Yuri V. Andropov.

As his health has worsened, he has been toasted and feted so many times. But this one, the official dedication of his own archive, meant more than all the rest to former Senator Jacob K. Javits. So he arranged it himself. ''He called me personally, and he said, 'Robert, can you make it? This is special,' '' Senator Robert C. Byrd, the minority leader and a Democrat of West Virginia, recalled. ''He's one of the few senators who calls me Robert. I said, 'Jack, you know I can't say no to you.' ''

A multimillion- dollar introduction of new products by three of the nation's biggest marketing guns, the Procter & Gamble Company, Nabisco Brands and Frito- Lay Inc., is trying to stir up the stagnant grocery store cookie market. The introductions also represent an attempt by Procter & Gamble and Frito-Lay, to enter - and capture - a healthy chunk of the $4.2 billion ready-baked store-bought cookie market now dominated by Nabisco. The new products are mainly designed to appeal to adults, and to the kind of people who prefer ''home style'' cookies but don't have the time to bake them. Dallas-based Frito-Lay, a subsidiary of Pepsico Inc. and the nation's undisputed king of salted snack foods, was the first into the fray. In May 1982 it rolled a line of 16 Grandma's Cookies into supermarkets in the Kansas City area. The cookies, generally soft, chewy versions of old favorites, now are available to about a third of the nation's population, primarily in the Southwest, Middle West, West and Southeast.