July 31, 1983

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.