What was going on when I was born?

SOME parents who chose to send their children to Public School 6 on the Upper East Side of Manhattan instead of to one of the neighborhood's many private and parochial schools were having second thoughts last week. The buses were so full that children had to stand; the school was short a kindergarten teacher; only three of the four school aides were on the job; some kindergartners were disoriented because their teachers did not guide them in their first trip to the cafeteria, and there was not enough staff to unpack all the textbooks. Yet even as these hitches occurred, the Alliance for the Public Schools was taking out newspaper advertisements and preparing to put posters on buses, urging people to support and use New York City's public schools. The movement to widen the constituency for public education has been growing in New York City and is spreading to other big cities. Such efforts arise out of concern that affluent whites have lost interest in urban schools as enrollments have come to be made up mostly of the poor and members of minority groups.

Because of an error by a research group, the Retirement Migration Project, an article on the Style page April 2 about the mobility patterns of the elderly was incorrect. There has been no significant reversal in the migration of those over 60 to small towns and rural regions. An article explaining the error appears on page C12.

China showed off its arsenal of modern missiles for the first time today in celebrating 35 years of Communist rule. The unusual military display was the highlight of the annual parade marking the Communist takeover of the mainland in 1949. In a speech, Deng Xiaoping, the Chinese leader, called for military preparedness and for peaceful reunification with Taiwan, the Nationalist-ruled island province. The last occasion on which the military took part in the annual parade through Tian An Men Square in downtown Peking was a quarter century ago. At that time, the Chinese did not yet have a modern missile force.

The Supreme Court, opening its new term, turned its attention today to the First Amendment's guarantee of freedom of speech. The Justices agreed to hear cases involving the definition of obscenity, the right to speak in favor of homosexuality, and the right of lawyers to seek clients for specific cases. In another First Amendment case, involving the free exercise of religion, the Court agreed to decide whether a state can deny a driver's license to a person who refuses on religious grounds to have a photograph taken. The Court sidestepped several civil rights controversies. It declined to intervene in the court-supervised desegregation of the St. Louis schools and refused to hear a challenge to a Miami ordinance setting aside public works contracts for black construction firms.

United States Justice Department officials, acting under a new extradition treaty with Italy, yesterday ordered the arrest of 28 Americans and Italians wanted in connection with Italy's major crackdown on the Sicilian Mafia. Rudolph W. Giuliani, the United States Attorney for the Southern District of New York, described the suspects as ''high level'' organized-crime figures involved in the multibillion-dollar international heroin trade. He said they faced Italian charges of murder, drug trafficking and racketeering. Four of the 28 were said to be in Federal custody in a related case. Sixteen more, Mr. Giuliani said, have arranged to surrender to Federal authorities today in Brooklyn, Newark, Illinois, Michigan and Wisconsin. The remaining eight, he said, are being sought.

The United States and Nicaragua have reached an impasse over a peace plan for Central America and appear headed into a period of increased tension, Reagan Administration and Nicaraguan officials said today. The two Governments exchanged accusations today about the peace plan and the legitimacy of elections planned in Nicaragua next month. Nicaragua's head of state, Daniel Ortega Saavedra, said in an interview at The New York Times that the Sandinistas were unwilling to accept any modifications in a regional peace treaty proposed by four Latin American nations last month and endorsed by Nicaragua 10 days ago. ''Any modifications that might be submitted would only destroy the document,'' he said.

The Bank of England today took over the banking subsidiary of Johnson Matthey P.L.C., one of the world's leading gold traders, to prevent disruption of the internationally important London Gold Market. The takeover, arranged in secret meetings over the weekend that kept key Johnson Matthey executives working virtually around the clock, came after outside auditors had drawn attention to the likely default of a number of major commercial borrowers from the subsidiary, Johnson Matthey (Bankers) Ltd. The Bank of England and Johnson Matthey said today that providing for the problem loans would have nearly wiped out the bank's capital. The rescue operation was the Bank of England's first in almost a decade. The last such effort was required to bail out small secondary banks that ran into trouble when property prices plunged after several years of speculation.

''This is a historical case, making it possible to rip apart the Sicilian Mafia.

The Italian police continued their roundup of organized- crime figures today as the authorities hailed the confession of an important Mafia figure as a political and psychological breakthrough in the fight here against racketeering. The arrests also spread to the United States. In Manhattan, Rudolph W. Giuliani, the United States Attorney for the Southern District of New York, said the Italian authorities had requested the arrest and extradition of 28 Americans and Italians on murder, drug and racketeering charges. Mr. Giuliani described the case as having ''tremedous repercussions'' for criminal investigations in the United States.

In a shift that startled the retailing industry, James M. Guinan resigned yesterday as president of Bloomingdale's after only six months in the job to become chairman and chief executive officer at Caldor Inc., the big Connecticut-based discount store chain. The 52-year-old Mr. Guinan, already meeting employees yesterday at Caldor's offices in Norwalk, said in a telephone interview, ''I took the job because I have never enjoyed retailing as much as when I was chairman of the Gold Circle discount stores.'' Although he conceded that his decision ''could have come at a better time,'' he said that ''opportunities like this crop up only once in a while.''

TUESDAY, OCTOBER 2, 1984 International China displayed its first ICBM's in a military parade in Peking marking the 35th anniversary of Communist rule. The military section of the parade included intercontinental missiles capable of delivering nuclear warheads, submarine-launched missiles and self-propelled howitzers never shown before in public. (Page A1, Column 3.) Nicaragua's rejection of changes in a peace plan for Central America has led to an impasse with the United States that threatens a period of increased tension between the two countries, Reagan Administration and Nicaraguan officials said. Nicaragua's head of state, Daniel Ortega Saavedra, said in an interview in New York that the Sandinistas were unwilling to accept any modifications in a regional peace treaty proposed by four Latin American nations last month and endorsed by Nicaragua 10 days ago. (A1:1.)

New York, New Jersey and Connecticut, seeking alternatives to costly prison construction programs, have intensified their search for other ways to ease their critical problems of prison overcrowding. More and more prisons will have to be built in the three states, according to criminal-justice specialists, unless the states change their sentencing laws to stem the flow of inmates entering prison and expand alternative programs to keep out of prison some of the people convicted of nonviolent crimes. New York and Connecticut, for example, are studying changes in their sentencing laws. New Jersey has begun releasing selected prisoners who are closely supervised by probation officers while they live at home and hold a job. Such approaches, state officials said, demonstrate an increased awareness of how the different parts of the criminal-justice system - prosecutors, judges, prison officials and probation officers - can affect one another and have an impact on the problem of prison overcrowding.