What was going on when I was born?

CHOOSING a comfortable armchair is a project that requires thought. Real comfort has as much to do with your own sitting habits as it does with the chair's shape. When considering the possibilities - and trying out a chair is mandatory before buying it - think about how you sit: Do you position yourself upright or in a sprawl? Do you cross your legs or stretch them out? Do you curl up, feet tucked under? What will you be using the chair for principally - watching television, reading, for social gatherings? If you are as likely to sit on the arms as on the seat, look for a chair with arms of substance. As in all upholstered furniture, inner construction has a lot to do with comfort. When shopping ask the sales clerk for specific information and turn the chair upside down to inspect it.

Columbia University graduated 7,173 students yesterday in ceremonies interrupted briefly by the walkout of about 200 students and faculty members opposed to the university's investments in companies operating in South Africa. The protesters, many with signs reading ''Divest Now'' pasted on their mortarboards, held what they called an alternative commencement on the steps of Hamilton Hall, 30 yards from the main ceremony on the school's central plaza and the scene of a three-week demonstration that ended last month. Among the protesters were 15 seniors whose diplomas had been withheld because they had participated in the earlier demonstration. The walkout began just as Columbia's president, Michael I. Sovern, began his commencement address.

The Allied Corporation, one of the most rapidly expanding automotive and aerospace companies in the nation, announced the biggest industrial merger in history yesterday, agreeing to buy the Signal Companies, another major aerospace producer, for nearly $5 billion in cash and stock. The deal, unanimously approved by directors of both organizations, will make the new company one of the biggest aerospace contractors in the world. It will operate under the name Allied Signal, with headquarters in Morris Township, N.J., Allied's present home. Edward L. Hennessy Jr., chairman and chief executive of Allied, who will head the new company, said of the deal, ''We're going to be in every airplane that flies.''

''We should not forget the time it took to reach agreement on the Austrian treaty.

The chairman of the State Senate Investigations Committee said today that he would hold public hearings on the operation of the New York City Police Department because of recent charges of brutality. At the same time the Cuomo administration is considering empaneling a Moreland Act Commission - an investigative body with sweeping subpoena powers - to examine accusations of brutality by police departments not only in New York City, but also around the state, according to administration officials. Also today, the United States Attorney for the Eastern District of New York, Raymond J. Dearie, announced that Federal prosecutors and the Federal Bureau of Investigation were investigating reports of torture and beatings at a Queens precinct station house. He said a Federal grand jury would look into the allegations.

The run on Maryland's privately insured savings and loan associations eased today. But the $1,000-a-month limit on withdrawals imposed late Tuesday by Gov. Harry R. Hughes caused widespread confusion. Throughout the state, savings institutions reported a sharp drop in the number of depositors waiting to withdraw their money. Meanwhile, the Governor disclosed today that Citicorp and the Chase Manhattan Corporation were negotiating with a team of state officials to acquire some Maryland thrift units.

President Reagan today approved the main elements of an ambitious plan to revise the Federal income tax system, Administration officials said, but the White House delayed the public release of the plan until May 28. In his plan for the most thorough overhaul of the tax code since World War II, Mr. Reagan adopted three rates of taxation for individuals - 15 percent, 25 percent and 35 percent -and the abolition of many deductions and so-called tax breaks, the officials said. The plan is intended, according to the President's advisers, to assure that all Americans pay their fair share of taxes. In a surprise move, however, the President decided to reduce the top rate on capital gains to 17.5 percent, a proposal that would primarily benefit affluent taxpayers. 2 Big Issues Remain Open There are now more than a dozen tax brackets, ranging from 11 percent to 50 percent, and the maximum rate on capital gains is 20 percent. Advisers who held their final tax meeting with the President this morning said two main issues remained open for discussion: the level of the personal exemption and the details of a minimum tax on corporations.

The Bankers Trust Company cut its prime lending rate yesterday by half a percentage point, to 10 percent. The move, which analysts expect other major banks to follow soon, means that the prime rate will be at its lowest level since 1978. This should provide a boost to the economy and make it easier for many businesses and debtor nations to repay their loans.

An article in Metropolitan Report on Tuesday about the upstate house where Ulysses S. Grant died - in Moreau, in northern Saratoga County -misstated the visiting hours. At present, visitors can tour the house only by appointment, which can be made by calling (518) 584-2000. From May 25 through Labor Day, the house will be open Wednesday through Sunday from 1 to 5 P.M. After Labor Day, the house will be shut.

A BMT subway train bound for Coney Island derailed yesterday morning, injuring 21 people and causing two fires that interrupted service on five lines between Brooklyn and Manhattan throughout much of the day. Transit Authority officials estimated that thousands of people had to change their travel plans. About 550 passengers were stranded underground on trains for more than an hour. A southbound N train was pulling out of the DeKalb Avenue station in downtown Brooklyn just before 10:15 when the second car of the eight-car train jumped the track, according to transit and fire officials. The car continued 120 feet, striking the electrified third rail and smashing into a track divider, the officials said.

Many black and Hispanic New Yorkers say that they are dissatisfied with their local schools and hospitals and that they are treated unfairly by the police and the courts, according to a New York Times/WCBS-TV Poll. Moreover, only a fifth of all the New Yorkers polled say the courts generally treat every racial group the same. And about a third of the white respondents say the police often engage in brutality against black and Hispanic citizens. But the complaints by members of minority groups that the city is not paying adequate attention to their needs do not appear to be affecting the mayoral campaign much. With the Democratic primary election still almost four months away, Mayor Koch holds a commanding lead over his two closest challengers, City Council President Carol Bellamy and Herman D. Farrell, an Assemblyman and the Manhattan Democratic leader, the poll found.

A small strike, barely noticed by most Americans, has created a severe strain in the long relationship between Israel and the American labor movement, to the point where the Israeli Prime Minister has now intervened to force a settlement. The strike, by the machinists union against El Al, the Israeli state airline, enters its 15th month today. The airline has continued operating at Kennedy International Airport and at its Manhattan office despite the walkout. The confrontation has triggered bitter charges of strikebreaking against the airline and threats that the labor movement will sell millions of dollars of Israel Bonds unless the strike is settled.