What was going on when I was born?

Guido Calabresi's ''Tragic Choices'' class at the Yale Law School deals with such vexing issues as organ transplants, population control and war. But in his first lecture of the semester today, Mr. Calabresi, who was about to be named the school's new dean, talked to the overflow crowd about other things. He gave them his office hours: whenever they feel like talking to him, any time the light in Room 233 is on. He gave them his home phone number, recalling how a distraught student once called at 3 in the morning to report he had left his torts notes on the New Haven Railroad. And he gave them a bit of advice.

Because of a mechanical error in some editions yesterday, an article about the New England office of the Anti-Defamation League of B'nai B'rith - and a list it circulated, protested by the Middle East Studies Association - omitted a paragraph.

The excess of American imports over exports shrank a little in December, but for all of 1984 the nation's trade deficit grew to a record $123.3 billion, the Commerce Department reported today. That dwarfed the prior record, set in 1983, when imports topped exports by $69.4 billion. In an uncommonly somber assessment of the merchandise trade figures, Commerce Secretary Malcolm Baldrige predicted still another record trade deficit for this year. Speaking of December's results, he said, ''Some of the improvement may have been temporary.''

Amid the nation's economic anxiety about becoming uncompetitive in world markets - a fear intensified by the $123 billion trade deficit reported yesterday for 1984 - the good news is that American exports are rising again after a two-year pause. Especially in high technology, American companies showed that they could overcome the adverse price effects of a rising dollar, and still sell more products abroad. Exports rose 8.7 percent last year, although imports outstripped them by jumping 26.4 percent and producing the record trade gap. Troubled exporters, such as the Caterpillar Tractor Company of Peoria, Ill., which have had to slash employment because of faltering sales and mounting losses, get most of the attention. But other sectors are booming: computer exports, for example, rose about 28 percent last year and broadcasting apparatus soared 20 percent.

''In private life - perhaps even more than in public life - I can speak out clearly on behalf of such shared foreign policy objectives as restoring and preserving American strength, supporting democracy and independence in the Hemisphere, defending our friends, our principles and our interests in the Middle East and elsewhere.'' - Jeane J. Kirkpatrick. (A6:4.)

The only clues that the city's official directory offers about Dr. Elliot M. Gross's job are contained in two sentences: ''The Chief Medical Examiner shall be a doctor of medicine and a skilled pathologist and microscopist. Office is open all hours of the day and night, every day in the year.'' The directory does not, however, describe another aspect of the office that was an open secret in law-enforcement circles but had not been a matter of public debate until allegations about the Medical Examiner were raised in The New York Times this week: The office is a political hybrid whose role in the criminal- justice system is fraught with potential conflicts. The allegations that Dr. Gross produced misleading or inaccurate autopsy findings, including reports on deaths of people in police custody, have prompted city and state investigations to re-examine the special relationships that affect the Medical Examiner's office. For one thing, the office operates in a unique partnership with prosecutors, but the partnership depends upon the credibility of its independent professional judgments on the cause of death in accidents, suicides and murder cases.

The Reagan Administration announced today that it was halting new arms sales to the Middle East for several months while it prepared a ''comprehensive review'' of the connection between the sales and peace and stability in the region. It was the first time in the memory of senior State Department officials that there had been a deliberate decision to suspend new arms sales to all Middle Eastern nations since the United States became a major supplier in the 1960's. The officials said the decision had been made primarily to avoid an early clash with some members of Congress over a contemplated large-scale sale of F-15 aircraft and other equipment to Saudi Arabia. Concern Voiced in Congress Supporters of Israel in Congress have expressed concern that arms sold to Saudi Arabia and other Arab countries not at peace with Israel could be used against the Israelis in a future Middle East war. The Reagan Administration has supported arms sales to Saudi Arabia to help protect it against Iran.

Stock prices, particularly those of over-the-counter issues, continued their climb yesterday in hectic trading. But the closely followed Dow Jones industrial average eased from the record it set on Tuesday. The Dow average of 30 blue-chip stocks closed at 1,287.88, off 4.74 points from Tuesday's high of 1,292.62. In the first hour, the Dow reached 1,299.36, close to the critical 1,300 point, but then fell back.

In a major legal decision with broad implications for corporate directors, the Supreme Court of Delaware has found that directors of the Trans Union Corporation breached their fiduciary duty to shareholders when they agreed in 1980 to sell the company to the Marmon Corporation for $688 million. The directors, the court said in a 3-to-2 ruling announced Tuesday, acted too quickly and did not seek enough information to make a responsible decision. Another Delaware court will decide if the $55 price paid for each of the Trans Union shares was too low. If so, the 10 directors, including Jerome W. Van Gorkom, Trans Union's now-retired chairman and chief executive officer, will have to pay the difference on more than 12 million shares, the Delaware court decision said.

A few weeks before the gas leak at the Union Carbide factory, it had been granted an ''environmental clearance certificate'' by the state pollution control board. It was a routine clearance required by the central Government of India, and it was readily granted since, in the words of a board official, ''only slight modifications were needed'' in the plant's emission controls. In fact, the plant was soon to suffer a chemical reaction that spewed lethal methyl isocyanate gas across this central Indian city in the early hours of Dec. 3, leaving more than 2,000 dead and 200,000 others injured. The aftermath has brought much soul-searching and finger-pointing over who was ultimately responsible for the tragedy. Plant workers, technical experts and former Union Carbide officials have described a deterioration of safety standards at the plant that, they say, helped provoke a disaster.

In recent years Congress has tried to expand the income that is subject to tax, and that effort shows up in several ways on 1984 returns. Social Security recipients and disabled retired people, for example, will find that Congress has chipped away at the 45-year-old tax exemption for Social Security benefits and the partial exclusion for disability payments. In addition, taxpayers who had big jumps in income last year will find that the ''income averaging'' method of calculating tax liability is now far less useful in paring tax bills. At the same time, the Internal Revenue Service will be doing considerably more cross-checking this year to make sure that taxpayers are reporting all of their income, including state and local income tax refunds paid to taxpayers who itemized deductions last year. Bolstering the Trust Fund The new tax on Social Security benefits, which is intended to affect only middle- and upper-income recipients, stems from the Congressional effort to shore up the Social Security system. About $2.9 billion is expected to be raised in the first year by the tax. It will be collected by the I.R.S. and passed along to the Social Security trust fund.

After months of bargaining, negotiators for the Metropolitan Transportation Authority and its largest supervisors union have reached an agreement to allow 500 to 800 employees to join management ranks, according to union and transit officials. Under the agreement, which must be ratified by union members, management will also gain the power to assign thousands of unionized supervisors their jobs, the officials said. Until now, these employees have been able to pick the jobs they wanted based on seniority. The agreement is the latest of several steps that will vastly increase management's power by creating up to 2,000 jobs that are to be filled by nonunion employees outside the Civil Service system.