What was going on when I was born?

Eighty-four suspected illegal aliens, many of them crowded into a tractor-trailer truck, were seized in the South Bronx yesterday after shots were fired without warning at two police officers responding to a report that ''suspicious persons'' were getting out of the truck. Fifty-one of those arrested, including 14 women, were still in the truck, in which all 84 had allegedly traveled for nearly three days. Henry S. Dogin, district director of the Immigration and Naturalization Service, said two men - identified as Roopnarine Singh, a resident alien from Guyana, and Efrain Vega, a United States citizen from Puerto Rico - were arrested on charges of unlawful transportation of illegal aliens in the United States. Said to Be From Mexico Mr. Dogin said the 83 Dominicans and one Guatemalan seized in the roundup were reported to have entered El Paso from Mexico late last Friday or early Saturday and to have packed into the trailer for the trip to New York.

Petro-Canada, the Government-owned oil company, is in the final stages of an agreement to acquire Petrofina Canada Ltd. from Belgian interests for $1.2 billion (in American funds), the two parties reported today. The acquisition would be the first breakthrough in the Government's campaign, announced last October, to end foreign domination of the country's oil and gas industry. Petro-Canada would acquire the Belgian parent's 71 percent interest in Petrofina, one of the smallest of the foreign-owned oil companies operating in Canada.

They took places at the head of classes yesterday, sitting in for the teachers who had moved out. Some of them just milled about in the hallways. They were the parents of students at the largely white annex of Intermediate School 231 in Rosedale, Queens, and they said they would fight to keep their school.

President Reagan, in an action that showed his determination to move away from the Carter Administration's emphasis on human rights as a key factor in foreign policy, agreed in a meeting today with President Chun Doo Hwan to normalize relations with South Korea. Mr. Reagan specifically promised Mr. Chun, whose human rights policies were severely criticized by the previous Administration, that the 39,000 American troops stationed in South Korea would remain there. Following what the White House called a ''friendly'' meeting between Mr. Reagan and Mr. Chun, a senior State Department official made it clear that military ''security,'' not Mr. Chun's domestic policy, was now the main concern in relations between Washington and Seoul. Congressional aides said the Administration had asked Congress to delay publication of a report on human rights violations in nations around the world to avoid embarrassing President Chun. (Page A6.)

The Wells Fargo National Bank charged today that it had been defrauded of $21.3 million by a group of sports promoters and companies that used the name of the former heavyweight boxing champion Muhammad Ali. Sources in the Federal Bureau of Investigation said they believed that if the allegation is true, the fraud is one of the largest in the history of American banking. Mr. Ali, who has said that he allowed his name to be used by an organization called Muhammad Ali Professional Sports Inc., known as Maps, but was not involved in the management or control of it, has not been accused of participation in the alleged fraud. In a lawsuit filed today in the Los Angeles County Superior Court, Wells Fargo charged that the fraud ''was accomplished by internal manipulation of funds involving 13 separate accounts.''

CRUSHING caseloads and declining financial support are forcing police laboratories around the country to search for fast and effective new techniques for analyzing clues and solving crimes. Some of the more sophisticated tools of modern science have been pressed into service, and analytical techniques in today's crime labs are hundreds of times faster and more revealing than those in use a decade ago. Because the Federal Bureau of Investigation has the most advanced crime laboratory in the country, it is often asked by state and local police departments to assist in difficult cases, and it is in these that the new techniques are proving invaluable. One local police force was stumped by a murder in which there were only charred remains of the victim. The police believed that the dead man's wife had probably strangled him with a rope and then burned the body, but since she was so much smaller than her robust husband it seemed unlikely she could have overcome him unless he had been incapacitated in some way.

IN 14th-century Yemen, then a thriving place along trade routes to the Orient, there was a king with an intellectual bent. He wrote numerous scientific tracts, including one dealing with the cultivation of grains, and was knowledgeable in health and astronomy. But his magnum opus was a six-language dictionary, a work of impeccable scholarship. He compiled some 1,200 familiar and important words in Arabic and then, in parallel columns, gave the words of comparable meaning in four and often five other languages - Persian, Turkic, late Byzantine Greek, Cilician Armenian and Mongol. It was a striking prototype of today's multilanguage dictionaries.

Your TaxesA Guide to Preparing 1980 ReturnsSecond of 12 articles.- By DEBORAH RANKIN Aside from income, an individual's tax rates are determined by filing status - the I.R.S. term for a person's marital status. The rates differ considerably, depending on whether a person is single, married, separated, divorced or living with someone. Married people filing jointly generally pay the lowest rates, while married people filing separately - for example, those who have informally separated - pay the highest. Single taxpayers and heads of households -unmarried taxpayers who are supporting certain relatives or foster children - pay rates somewhere in between.

In an attempt to flush out the billions of dollars in currency that circulate here in an underground economy, the Government of India is offering high-yield bonds that are to pay handsome rewards to tax evaders. The program announced last month has drawn indignant condemnation from some politicians and economists, who contend that by effectively paying dividends and bonuses to hoarders and black marketeers, the Government is debasing any respect for law. On the other hand, some economists have attacked the proposal as not offering enough inducements to drive much concealed money out of what is usually described as an alternate or parallel economy. This economic network is supported by the accumulations of undeclared incomes gathered since World War II. The circumvention of taxes and commercial regulation is widespread and the movement of socalled black money has proved an easy challenge for Indian entrepreneurial ingenuity.

Rain swept across the New York metropolitan area yesterday following last month's record dry spell, but water engineers said the storm, while welcome, had a minimal effect on the region's water shortage. They warned that residents coping with mandatory cuts in water use in New York City, northern New Jersey and southwestern Connecticut must not relax their vigilance about conservation. ''If people stop conserving water, it would bring tragic consequences,'' said John Cunningham, a spokesman for New York's Department of Environmental Protection.

In his first major official act, Secretary of Education T.H. Bell today revoked proposed regulations that would have required public schools to teach foreign-speaking students in their native languages. Mr. Bell, remarking he was seeking to ''telegraph a message of change to the American people,'' said that the bilingual education rules proposed in the final months of the Carter Administration were ''harsh, inflexible, burdensome, unworkable and incredibly costly.'' The regulations would have required school districts with more than 25 foreign-speaking students to offer the students instruction in their native languages, as well as in English. Any variance from this would have required a waiver by the Department of Education.

The Dow Jones industrial average plunged 15.10 points yesterday as prices of former stock favorites continued to erode. It marked the eighth decline in the 10 trading sessions since President Reagan took office on January 20. The Dow cloped at 932.17, which was 38 points lower than its level on the Monday before Inauguration Day, when the sell-off began with a drop of 20.31 points. In contrast to last week's performance, when steel, chemical and other basic industry issues moved ahead, only one of the Dow's 30 components showed a gain yesterday. That was Alcoa, up 1 3/8, to 62 3/4.