What was going on when I was born?

CROWD counts are notoriously unreliable. They are also irresistible. Someone, for example, could not resist estimating the number of people in Southampton Town over the big Fourth of July weekend at 300,000, a figure that eventually found its way into local press reports. The 300,000 figure - about the same number of people as inhabited all of Suffolk County just 30 years ago, and almost seven times Southampton Town's present year-round population - might have been greeted with considerable skepticism had the evidence of this year's apparently unprecedented influx not been so highly visible in the Hamptons. ''It was a tremendous amount of people,'' said a spokesman for the Southampton Town police, who was careful, however, to avoid declaring a record. ''If you are looking for exact figures,'' he said, ''that's impossible.'' In some cases, exact figures were not necessary. Beach parking lots, for example, filled to capacity in both Southampton and East Hampton, told their own tale. In other cases, the figures were there: police activity in Southampton Town was up 16 percent over that reported for the holiday weekend last year; at Southampton Hospital, which serves the entire South Fork community, a total of 499 emergency cases were treated over the weekend, up 22 cases from a year ago.

YEAR-OLD Tara was the size of a child 12 months younger. Her head looked disproportionately small even for her little body, the slits of her eyes were shorter than normal and her smooth, tightly drawn upper lip lacked the vertical groove that usually runs between the nose and mouth. The child fidgeted, giggled and looked away as Gigi Smith, a speech pathologist at University Hospital here, showed her pictures of a cup, a knife, a window and a stove. Tara could not name a single object. Her language development, an indicator of intelligence, was comparable to a child half her age, Mrs. Smith concluded.

ALTHOUGH acid rain is one of the more prominent environmental concerns, its extent and its possible effects in the county remain uncertain. Opinions are often based more on speculation than on hard evidence, officials concede, because detailed information is scarce. Acid rain occurs when manmade pollutants - largely sulfur and nitrogen oxides, which some believe are emitted by coal-burning power plants - are transformed in the atmosphere into sulfuric and nitric acids. These, in turn, are carried back to the ground by rain or snow or fall back as dry particles. The residue, many scientists contend, has a devastating effect on freshwater ecological systems and plant life and may directly endanger human health. Others argue that not enough is known about acid rain and that its origins in industrial emissions has not been conclusively established. They hold that costly pollution controls might not alleviate the condition. Congress is considering acid-rain controls and the Federal Environmental Protection Agency has given high priority to the development of a program to address the issue.

With an eighth of a mile to go, seven of the best horses in the country were strung out across the stretch at Saratoga Race Track today and the Whitney Handicap was anybody's race. Island Whirl, trying to duplicate his front-running victory in the Hollywood Gold Cup, was clinging to his early lead; Sunny's Halo, the Kentucky Derby winner, had finally shaken loose from traffic and was closing on the rail; Linkage and Fit to Fight were not quitting after chasing Island Whirl, and Deputy Minister and Bold Style were closing fastest of all on the outside. But the winner at the wire was the one who had led all along. Island Whirl held off Bold Style by a desperate nose to win the 56th running of the Whitney, a race in which so many horses ran so well that few horsemen or fans could be disappointed. Sunny's Halo finished only three-quarters of a length behind the top pair, and Deputy Minister and Fit to Fight finished in a dead heat for fourth, another two lengths back.

Nine nervous nations met in Panama City over the weekend to seek a way out of the Central American imbroglio before armed conflict spread. Soviet freighters reportedly approaching Nicaragua with arms shipments, American naval units beginning to maneuver in the same waters and massing of troops on the Nicaraguan-Honduran border gave the meeting an air of urgency. The latest effort of the so-called Contadora group - Mexico, Panama, Venezuela and Colombia - to find a peaceful solution in El Salvador and ward off fighting between Nicaragua and Honduras involved a meeting with the Foreign Ministers of the five Central American states, Guatemala, El Salvador, Honduras, Nicaragua and Costa Rica. A major goal was an end to the involvement of outside powers.

Last fall, even though hospitalized by the illness that finally ended with his death in April, George Balanchine was still planning the ballet epic he had been thinking of, off and on, for some 40 years. Though it was never actually realized, few projects seem to characterize the idiosyncratic vision of this prolific choreographic genius as profoundly as the work that was to be titled ''The Birds of America.'' Would ''The Birds,'' as it became familiarly known, have been a ''Don Quixote'' or might it hae been an''PAMTGG,'' whose title referred to the airline jingle ''Pan Am makes the going great''? It is impossible to tell, of course, but it did promise to be a poignant testimony to Balanchine's affection for America, hisadopted country for the last half century. Set to a commissioned score by Morton Gould, a major portion of which was completed,the unfinished ballet lives today in the memories of those who worked with the choreographer as a thing of possible beauty, distinguished by the eminent practicality that made masterpieces of some of his most quixotic schemes.

The flow of military supplies to Salvadoran rebels from outside the country has been only a trickle for many months, according to officials here and in Washington. A senior Reagan Administration official, interviewed in Washington several days ago, said ''that's true'' when asked about reports that Salvadoran guerrillas were receiving only small amounts of ammunition and weapons from Nicaragua, where a Marxist-dominated junta controls the Government. The official also said the Salvadoran rebels had little need of such aid. (A State Department spokesman, disputing the reports, said ''significant amounts of logistics, ammunition and logistical supplies'' continued to arrive from Nicaragua by sea, land and air.)

TWO young lawyers, each of whom has spent half of his life in politics, are engaged in one of the toughest primary fights in the county - the struggle for the Democratic nomination for County Legislator in the town of Greenburgh. The contenders are Thomas J. Abinanti, 36 years old, a Town Board member since 1977 who has the bulk of official party support, and Paul Feiner, 27, an activist who is leaning heavily on a strenuous door-to-door campaign. The winner will face Reginald Marra, the 42-year-old Republican Mayor of Irvington. They are fighting to represent the new 12th Legislative District, a creation of the Republican-controlled County Board and its longcontested reapportionment plan. In redesigning all 17 legislative districts, it managed to divide largely Democratic Greenburgh into five parts.

GEORGE C. SCOTT, the actor, may have summed it up best in his screenp ortrayal of General George S. Patton Jr. Standing majestically on a h illtop in dress jodhpurs, clenching a riding crop at the side, he g azes across a battlefield that is littered with the bodies and s moldering wreckage of a tank battle. ''I love it!'' he cries. ''God help me, I do love it so!'' For General Patton, war brought on exhilaration and crisis occasioned his finest moments. But crises - and battlefields - come in many forms. And the victors who emerge from them elated are a breed apart. In business, they are a small group of professionals who thrive on turning around seemingly impossible situations, more akin to wartime generals or emergency room doctors than to their buttoneddown colleagues in banks and investment houses. Yet despite the fact that business bankruptcies soared 70 percent in the year ended March 31, these corporate fixers are so rare that there is not even a word for the trade they ply. One of the bestknown practitioners, Stanley Hiller Jr., even has difficulty explaining what he does. He describes it as ''R. & R. - the repair and rebuild business.''

tended gardens are in vivid bloom, and smiling tourists stroll and pose and snap photographs, just as they have done for 30 years. Inside the theater, one of the few in North America devoted to the classical repertory, the curtain rises nightly on ''Macbeth'' or ''As You Like It'' or ''Richard II.'' To a casual observer, the scene at the Stratford Festival in Stratford, Ontario seems to represent the business of Shakespeare as usual. In this case, however, the pastoral atmosphere is somewhat deceptive. Rocked by a bitter dispute that jeopardized its very existence only two years ago, the Stratford Festival is now trying to recover from the damage inflicted on its reputation, its company and its morale by what most of those involved agree was gross mismanagement.

The MX missile, touted by its defenders as an essential strategic weapon and a valuable bargaining chip, held its own last week. But it still hasn't quite cleared the Capitol Hill launching pad. Though the Senate, after two weeks of debate, voted for a $4.6 billion plan to deploy a first cluster of 27 MX's, opponents said another tough fight this fall was a certainty, when it's time to appropriate money for the missiles. ''It's a bad decision from a military standpoint,'' said Colorado Democrat Gary Hart, a Presidential prospect who had led an unsuccessful filibuster, ''a bad decision from an economic standpoint, and a terrible decision from the standpoint of national security.'' President Reagan said that the favorable MX votes -the House had approved deployment earlier - made progress in disarmament talks all the more likely.

IF the $3.2 billion Shoreham nuclear power plant existed only in a soap opera or a socially conscious feature-length movie, the last two weeks might well be hailed as the scriptwriter's ultimate triumph. Suddenly the already sizable cast of characters in the long-running drama over the nearly completed reactor swelled to include - in relatively major roles - one of the nation's largest defense contractors, two United States Senators, two Governors and a host of subordinates. But Shoreham is real, and the officials who have joined the debate in recent weeks are not matinee idols. Instead, their involvement reflects the way public attitudes have changed in the eight weeks since the Long Island Lighting Company proposed a 56 percent rate increase to pay for the 809-megawatt reactor. Only six months ago, the debate centered on questions that were framed with a sense of immediacy if not breathless urgency: whether the plant should open, whether it could be operated safely and whether Long Island could be evacuated in case of an accident. All those questions pitted Suffolk County - where County Executive Peter F. Cohalan said there was ''no way'' to evacuate loacl residents - against Lilco, which took the unprecedented step of filing an evacuation plan when Mr. Cohalan refused to do so.