What was going on when I was born?

''I enjoy proving the experts wrong.'' - Nicholas F. Brady, named to be United States Senator from New Jersey. (B5:4.)

An unexpected shortage of substitute teachers is troubling schools in New York City and other urban centers around the United States. It is forcing principals to search desperately each day for replacements for absent teachers and it often disrupts the normal education of students. Sometimes principals themselves take over classes because no substitutes are available. At other times, youngsters whose teachers are absent are required to spend the day sitting in the school auditorium because there is nobody to teach them.

The small symbol of the Republic is safe now, nestled to the body of its nursemaid 80 feet off the ground in the tower of a pine at the edge of Bear Swamp. Earlier today there was some doubt about their meeting, some fear the one might reject the other. Perhaps even kill it. Still, all went well, and now New Jersey's only pair of nesting bald eagles, which for six years have been unable to produce a viable egg, have a chick. The state wildlife officials who introduced the laboratory-born eaglet into the nest of its wild surrogate parents this morning hope that the chick will signal a resurgence of the species here.

Retail sales fell 0.5 percent last month, the Commerce Department said, and they are likely to stay sluggish in the second quarter, Commerce Secretary Malcolm Baldrige predicted. The results contrasted with a 2.6 percent rise in February that apparently only temporarily stemmed two previous declines. (Page D1.) February installment debt grew by only $75 million in February as consumers reduced credit purchases because of the recession. The rise, at an annual rate of gain of less than 0.5 percent, compared with an annual growth rate of 6.8 percent a year earlier. (D8.) The Fed tentatively decided to change the way it reports weekly money supply figures, shifting to a four-week moving average. The change is an effort to lessen the numbers' impact on financial markets. (D1.)

The Federal Reserve Board tentatively decided today to change the way it reports weekly money supply numbers, in an effort to lessen their impact on the nation's financial markets. The board, at an open meeting, reached a consensus to report each Friday afternoon the average of the most recent four weeks of money supply growth or decline, instead of changes in the money supply for the previous week only. The board said that it was also considering delaying the release time of money supply figures from the current 4:10 P.M. on Friday to 5 P.M. or later to be sure that most markets, including those on the West Coast, were closed before the figures were released. But there was no tentative decision on this issue. Under the current system, the Fed's money supply announcement sometimes affects late-afternoon trading in fixed-income securities, causing yields to rise or fall.

The Shiite Moslem clergymen around Ayatollah Ruhollah Khomeini, having crushed their moderate, secular opposition, are now themselves coming under sharp challenge from a yet more conservative group of mullahs. The behind-the-scenes power struggle is so severe, diplomats and other political analysts here say, that it has blocked action on three major issues facing revolutionary Iran: land redistribution, nationalization of foreign trade and, above all, the question of political succession when Ayatollah Khomeini dies. On one level, the differences are rooted in an important but somewhat arcane point of theological dogma, but the split also has practical political implications. As a result, the Ayatollah and his followers have now assumed the position of ''moderates'' and, in some fields, social reformers, while his opponents are seen as more tied to powerful, moneyed interests - landowners and wealthy bazaar merchants - and as even more stringent in their application of religious law in such fields as the role of women. Pro-Moscow Party Making Gains Even as the infighting is going on within the clergy-led Islamic Republican Party, which dominates the Government, the analysts say, members of the Moscow-oriented Tudeh Party, which has professed loyalty to Ayatollah Khomeini and adopted an Islamic guise, are gaining increasingly powerful roles in key ministries.

American banks have more than $9 billion on loan to the Government and residents of Argentina, and a spot-check yesterday showed that many were deeply concerned about the economic effects of Argentina's conflict with Britain over the Falkland Islands. For the most part, however, banking officials said that there was little that they could do except to sit tight and hope that the difficulties would be resolved quickly. ''We're conducting business as usual, but watching the situation with a very close eye,'' one leading New York banker said. Because of the banks' desire not to harm their long-term relationships with either Britain or Argentina, no banker was willing to speak for attribution.

Hopes for a breakthrough in the Falkland Island crisis faded today when Secretary of State Alexander M. Haig Jr. said after 11 hours of talks with British leaders that ''a number of substantial difficulties remain.'' Mr. Haig, who met with Prime Minister Margaret Thatcher and other officials, delayed a planned departure for Buenos Aires until Tuesday morning. A spokesman said that he had spoken by telephone with Argentine officials but that there were substantive differences still to be worked out. Although no official comment was made on the substance of the talks, the principal issue appeared to be the insistence by both Britain and Argentina on retaining some element of sovereignty over the islands, which were seized by Argentina from Britain on April 2.

Three CBS employees were shot to death last night when they stumbled upon the abduction of a woman in a rooftop parking lot on a pier on Manhattan's West Side, the police reported. The police identified the slain men as Leo Kuranuki, 54 years old, of Great Neck, L.I.; Robert Schulze, 58, of Clifton, N.J., and Edward Benford, 55, of Hawthorne, N.J. CBS said all three were engineering technicians employed by the television network. Chief of Detectives James T. Sullivan said the victims, who had just left work at the CBS Broadcasting Center at 524 West 57th Street, near 11th Avenue, were shot at about 6:15 P.M. as they went to their cars on the roof of Pier 92, a three-story steel-andconcrete structure that juts 900 feet into the Hudson from 54th Street and 12th Avenue. It was not known whether the men attempted to intervene in the abduction they encountered, but they were gunned down as they tried to flee from the lone assailant, who chased them across the roof, the police said. Then, with his apparently wounded kidnap victim, he sped away in a van down a narrow, twisting ramp, past witnesses and attendants in the Kinney System parking lot.

President Reagan plans to announce this week that he will soon propose legislation providing tax credits for families whose children attend private or parochial schools, White House officials said today. In the draft legislation, the officials said, a maximum tax credit of $500 would be phased in over three years, starting in 1983. The size of the credit would depend on a family's income, and families above a certain income level would not be able to receive it. Recipients would be able to deduct the credit directly from the amount of Federal income tax that they pay. A tax credit is more valuable than a tax deduction, which is subtracted from the income of an individual before determining how much tax is owed.

For as long as many people in the semiconductor industry can remember, Motorola Inc. has played Avis to Texas Instruments' Hertz. No matter how much harder it tried, Motorola has always been a relatively obscure second in worldwide sales to the Dallas giant, which prides itself on having invented the integrated circuit in 1958. Now, however, a tailspin at T.I. and momentum at Motorola have suddenly brought the runner-up within challenging distance of the leader, and the race is on. ''It's going to be fairly close from this point forth,'' said James Barlage, an industry analyst with Smith Barney, Harris Upham & Company. In 1980, Texas Instruments, with semiconductor sales of $1.6 billion, held a comfortable lead over Motorola, whose semiconductor sales reached $1.1 billion, according to Dataquest, a Cupertino, Calif., market research firm. But last year T.I. plummeted to $1.3 billion in semiconductor sales while Motorola managed a modest increase, to $1.2 billion, cutting the gap in this sector to a mere $100 million.

AMERICAN business schools are accused of training too many ''cold'' technicians who know a great deal about corporate strategies but too little about operations in the field where corporations ultimately succeed or fail. Their graduates, it is said, often hurt corporate morale by capturing top management positions denied to people with greater experience down the line. The source of these criticisms is Richard T. Pascale, a lecturer and consultant at Stanford University's Graduate School of Business who is co-author of ''The Art of Japanese Management.'' Mr. Pascale places the blame for these shortcomings primarily on the ways of American corporations, which influence the schools where they hire their new M.B.A.'s, masters of business administration, as their future managers. He speaks of the ''big brains'' who determine corporate strategies and the ''little brains'' who deal with line operations, and he attributes much of Japan's industrial success to the greater attention its managers pay to those little brains -the salesmen, customer representatives and production people, and ultimately the customers.