What was going on when I was born?

A projected meeting of Latin American nations to discuss the widening conflict in Central America has been postponed indefinitely, according to diplomats here. Instead, the diplomats indicated that a new initiative would be proposed soon by four of the region's governments. The meeting on Central America, which had been expected to take place this month in the Dominican Republic, would have included representatives of five Central American nations - Costa Rica, Honduras, El Salvador, Guatemala and Nicaragua - as well as observers from Panama, Mexico, Venezuela, Colombia and the Dominican Republic. The Latin American nations had planned to exclude the United States from the talks, a move to which the Reagan Administration did not object.

Thomson McKinnon Inc., though among the nation's 20 largest brokerage concerns, makes little noise on Wall Street. Competitors and analysts most often describe the company as reserved and conservative - ''the traditional wire house,'' said one. John J. Maloney Jr., the company's chairman and chief executive officer, puts little weight in such observations. ''Anyone who says that doesn't know much about Thomson McKinnon,'' he said Friday Last week, Thomson announced its intention to enter the banking business. If Federal regulators approve, it will acquire the First Federal Savings and Loan Association, a small thrift institution in Madison, Conn., in a cash transaction valued at $10.8 million. The deal would result in the first purchase of a savings institution by a brokerage firm.

An article in Postings in yesterday's Real Estate section misstated the starting time of a conference tomorrow on back-office space in New York City. The conference begins at 6 P.M.

Vietnamese soldiers herded Cambodian civilians into bunkers last week and threw hand grenades at them, according to Cambodians who said they had been victims or witnesses of such attacks. These statements, made in interviews today by 13 Cambodian civilians at a Red Cross hospital near this border town, were the first accounts supporting recent charges by a Cambodian insurgent leader that Vietnamese troops had deliberately attacked civilians in their drive against rebel forces near the Thai-Cambodian frontier. The civilians said the grenade attacks took place over three days, beginning April 3, at O Smach, a camp on the Cambodian side of the border. That was the day the Vietnamese fought their way into the camp; they completed its capture on April 4. No Figures on the Dead Those interviewed did not give figures on the total number of civilians killed but said most of the victims they knew about had survived. The insurgent leader said last week that ''several hundreds'' had been killed.

With only five days remaining before the deadline for filing Federal personal income tax returns, financial institutions in New York City and around the country are reporting a last-minute surge in depositors opening Individual Retirement Accounts to qualify for a deduction on 1982 taxes. ''They've really been coming in in waves, especially since April 1,'' said Cynthia Bailey of the Chase Manhattan Bank. Some other I.R.A.-sponsoring institutions have been reporting averages of 5,000 to 7,000 new accounts a day in recent weeks, as savers seek to beat the April 15 tax deadline. The institutions are encouraging this rush to open the retirement accounts in nationwide promotional campaigns. Big newspaper display advertisements and spots on radio and television are touting the investment and tax opportunities offered by I.R.A.'s.

Jordan said today that it had failed to reach an agreement with the Palestine Liberation Organization and would not enter American-sponsored peace talks on the basis of a plan proposed by President Reagan. The announcement was issued in Amman after talks between King Hussein and Yasir Arafat, chairman of the P.L.O., on a joint approach to the Reagan plan. According to the announcement, which followed a Cabinet meeting, the King and Mr. Arafat had reached an agreement to take immediate joint political action, but the P.L.O. later proposed ''a new course of action that differed from our agreement.'' P.L.O leaders in two Arab cities said there had been no such agreement. Won't Enter Talks Alone Having failed to reach a joint negotiating formula with the P.L.O., the Jordanian Cabinet said, King Hussein's Government was now removing itself from negotiations over the future of the West Bank and was leaving everything in the hands of the P.L.O. This scotched American hopes that Jordan would enter negotiations alone.

For the sixth weekend in a row, the New York metropolitan area got rain. And the rain yesterday was a heavy, soaking rain that made umbrellas more of a psychological than a practical aid, that turned front lawns into swamps, basements into pools and subway stations into dripping caves. More rain fell yesterday in New York City than on any day in April since 1874, the first year for which records are available, according to the National Weather Service. Fifteen families were evacuated from a Bronx apartment building, at 2311 Beaumont Avenue, in the East Tremont section, after a retaining wall collapsed and a mud slide crashed into the first-floor apartment windows. In Central Park, motorboats were dispatched to rescue drivers from cars stalled in waist-deep water on the 65th Street Transverse.

President Reagan said today that Jordan's apparent refusal to join any Middle East negotiations was ''an impediment'' in the search for a Middle East peace. But he said he remained ''very hopeful'' that progress could still be achieved on the basis of his seven-month old initiative. Speaking to reporters at the White House, Mr. Reagan said he had spoken by telephone today with King Hussein of Jordan and with King Fahd of Saudi Arabia and that all three agreed not to abandon peace efforts and that the latest problem in the quest for new Middle East negotiations was the fault of ''radical elements'' in the P.L.O. Mr. Reagan did not elaborate, but other officials said he was not referring to the P.L.O. chairman, Yasir Arafat, who is regarded here as a moderate, but to those in the P.L.O. opposed to any compromise and who appear to have blocked an accord with King Hussein. Meetings at State Department The initial intent of the Administration seemed to be to dispel reports from the Middle East that Mr. Reagan's initiative of last Sept. 1 was now dead. Meetings were held at the State Department this afternoon to discuss the situation and decide whether King Hussein should be invited to Washington or Secretary of State George P. Shultz should travel to the Middle East.

Computer scientists at New York University have produced the first successful version of a key program needed by the Defense Department to develop a standard computer language for the military. The success - by the team at N.Y.U.'s Courant Institute of Mathematical Sciences - helps open the way for the use of the new computer language, known as ''Ada,'' that the Defense Department has chosen to replace the hundreds of languages now in use. It is named after Augusta Ada Byron, Lord Byron's daughter, who is considered the world's first programmer because of her work with the 19th-century British mathematician, Charles Babbage, who designed a calculating machine. A single language would save the Pentagon billions in training and programming costs and is expected to make the military's computer systems more effective by ending the electronic chaos that now prevails.

Four of golf's longest hitters, Ray Floyd, Craig Stadler, Seve Ballesteros and Tom Watson, each of whom has won a Masters tournament, moved their heavy artillery into position for Monday's final-round shootout in the 47th Masters. Floyd, the easy winner of the 1976 Masters, and Stadler, the defending champion, were tied for the lead at six-under-par 210 following today's third round on the Augusta National Golf Club's 6,905-yard course; Ballesteros, the sometimes wild but always long golfer from Spain who won the 1980 Masters, was a stroke back at 211; Watson, the 1977 and 1981 winner, was another shot back in a tie with Jodie Mudd at 212. Mudd, finishing his first year as a pro, is about as long off the tee as the other four leaders, although he has not won a professional tournament. The rain-delayed Masters that finally had a round in clear but windy weather today, will possibly have a real long-driving exhibition in the Monday conclusion because Floyd and Stadler will be the last twosome to go off, right behind Ballesteros and Watson. With the wide fairways and no real rough, Augusta National tempts those who tend to let out shaft. And it is necessary to be long to win here. Mudd precedes these four.

The Board of Education will get as much as $150 million more than expected for the next school year, Deputy Mayor Robert F. Wagner Jr. said yesterday. Mr. Wagner, who was selected Saturday as the city's new Schools Chancellor, said the extra money would allow the system to increase its teaching staff by as many as 2,100 instead of losing nearly 3,400, as City Hall expected in January. The Deputy Mayor still must obtain a waiver from the State Education Commissioner because he does not meet all the qualifications for the chancellorship as set out in state law. He said, however, that he was confident this requirement would pose no problem. Mr. Wagner's departure from City Hall will leave Mayor Koch with two Deputy Mayors, Nathan Leventhal and Kenneth Lipper. Mr. Koch said he planned to divide Mr. Wagner's duties primarily between those two aides. (Page B4).

It has been more than three centuries since the Pequot Indians so dominated this region that the first white colonists named the river here the Pequot and their settlement Pequot Town. Soon those homesick settlers renamed the river Thames and the town New London. They fought the Indians, slaying several hundred in one battle in 1637, and sold some into slavery and confined the rest to a series of reservations, the last one on rocky soil here. And in 1856, acting under a state law entitled ''An Act for the Preservation of Indians and the Preservation of Their Property,'' a county court sold most of the reservation: the ash and oak forest full of game, the marshes, the tribal burial ground.