What was going on when I was born?

Several experts on Social Security today criticized President Reagan's latest statements about the program, saying that his analysis of benefits in relation to payroll tax contributions was misleading. In a television interview made public Friday, Mr. Reagan said he would not ''pull the rug out'' from under people now receiving Social Security benefits. But he said, ''There is a possibility - well, probability - that many people, young people now paying in, will never be able to receive as much as they're paying.'' Mr. Reagan did not elaborate. In an interview last March he said that demographic changes were ''leading inevitably toward another day of reckoning'' for such benefit programs.

MICHELLE MILBERG of Westport has arranged photographs of her family, including Samantha the poodle, on her wall and placed a Michael Jackson poster above her bunk. Peter Katz of Fairfield has kissed his parents in the parking lot for the sixth summer in a row and bid them goodbye until visiting day. And Norman Feitelson is sitting in his office, reflecting on the rubber hamburgers and phony pickles he has been served and the 15 turtles that were deposited in his screened porch one night last August. He is wondering what this season's pranks will be. Summer camp has started, the season for unpacking trunks stuffed with suntan lotion and insect repellent and for being grouped into Indian tribes with names like Iroquois and Pequot.

The record book now shows that Martina Navratilova has beaten Chris Evert Lloyd in 12 straight matches, but the entry for the Wimbledon final today deserves an asterisk because the challenger raised a waning rivalry to a new level. The 7-6, 6-2 victory, achieved in glorious sunshine before a Centre Court crowd fizzy with excitement, gave Miss Navratilova her fifth Wimbledon singles title, her third in a row, and evened her 11-year rivalry with Mrs. Lloyd at 30 victories apiece. Miss Navratilova, who earned $133,000 for the triumph, has now won five consecutive Grand Slam tournaments and 218 of her last 223 matches. In the men's final Sunday, the defending champion, John McEnroe, who has lost only one match this year, will play Jimmy Connors, the winner here in 1974 and 1982.

WASHINGTON THE selection of a running mate is traditionally a way to heal a party's wounds. But last week the process itself emerged as a potential threat to Democratic unity and Walter F. Mondale's hopes for a peaceful convention. Throughout the spring, divisions grew naturally out the primary process. But this new strain is mainly of Mr. Mondale's own making. It was the former Vice President who invited the parade of Vice Presidential aspirants, in which last week Representative Geraldine A. Ferraro of Queens, Mayor Henry Cisneros of San Antonio and Governor Martha Layne Collins of Kentucky make the trek to North Oaks, Minn. The ostensible reason was to give Mr. Mondale a chance to look over the field - seven so far. But the process has prompted intense lobbying from factions eager to influence him and may, in the end, limit his freedom of choice.

IN Pratt & Whitney's sprawling machine-tool factory here, an unsettling quiet has set in. Many of the assembly bays in the hangar-like room stand empty, parking spots are easy to come by in the company lot and workers hover over aging equipment that has been dulled by decades of use. Trounced by imports and struggling to fatten an anemic order book, the plant here, like the rest of the machine-tool industry, is grappling with its worst crisis since the Depression. Business should have improved markedly by now in this once-thriving industry, which makes the high-precision metal-cutting tools essential for producing such things as automobile fenders, airplane fusilages and the machines needed by other industries. But the business continues deep in the doldrums, with no letup in sight. As many other industries surge ahead, propelled forward by the country's booming economic recovery, the machine-tool industry is still in crisis. Orders, which analysts estimate could reach about $2.8 billion this year, are stuck at half their 1979 levels and employment, at 67,000 workers, wavers around 30 percent below its peak at that time. While American industry is operating at over 80 percent of capacity, machine- tool manufacturers are treading water at just 60 percent of capacity. Imports have become such a significant factor that they now account for almost 40 percent of the market, double the level of only five years ago. Although there has been a modest rise in orders in the last year, orders remain so weak that executives and analysts are starting to realize that the industry is undergoing a sharp, and perhaps irreversible, contraction.

NASSAU and Suffolk Counties are adopting a state-controlled, computerized system that local officials believe will enlarge the pool of prospective jurors. As a result, an increasing number of Long Island residents will enjoy the privilege - or suffer the inconvenience, depending on how they look at it - of jury duty in coming months. In Suffolk, the change coincides with a recent judicial finding that held that the current county system has discriminated against blacks between the ages of 18 to 21 by not calling them in sufficient numbers to jury duty. In the ruling, County Court Judge Stuart Namm also questioned whether the Suffolk system assured that younger residents were summoned for jury duty in a wholly random manner as the law requires. Under the new system, due to begin soon, a master list of prospective jurors will be compiled for the commissioner of jurors in each of the two counties by the State Office of Court Administration, which was set up in 1977 to apply computer technology to the staggering clerical tasks that courts confront. Traditionally, the county commissioners, using manual methods, have relied heavily on local lists of registered voters to cull jurors. The state system, using computers to discard duplicate names, will draw prospects from among registered voters, licensed drivers and state taxpayers.

WASHINGTON THE Soviet Union and the United States, after a week of intense jockeying, now find themselves closer to talks on space weaponry than officials on either side imagined possible a month ago. But even if the two sides were to face each other across the table this September in Vienna, as Moscow has proposed and as the Administration says it has ''accepted,'' actual agreements are not on the horizon. Each recognizes that substantive positions on limiting these weapons are far apart, and that after three years of stalemate in the relationship as a whole, neither has much credibility with the other. The Soviet Union is seeking an agreement banning antisatellite and space-based weapons which Administration experts are convinced would be unverifiable. The Reagan Administration sees the proposal as a trick to try and head off new American weapons programs. The Russians, in turn, say American responses are a ploy to gain space superiority and help the President's re-election.

The Mets rose to dramatic heights last night in Shea Stadium when they routed Mario Soto inside four innings, whipped the Cincinnati Reds, 14-4, and climbed back into first place in the National League's East. They kept a crowd of 35,004 roaring as the rookie Dwight Gooden outpitched Soto while the Mets made a shambles of the heralded ''strikeout duel'' between the two pitchers. They also won their fourth straight game and the eighth in their last nine, and they produced some of their most rousing feats in a rousing season: The 14 runs were the most they had scored in a game in five years, their 18 hits were the most they had delivered this season and their seven runs in the fourth inning equaled their best time at bat this season. First Victory Over Soto They defeated Soto for the first time, after he had beaten them seven straight. They ended his eight-game winning streak in the league this season. And they made him a losing pitcher for the first time since April 13.

Tyrell Biggs of Philadelphia and Pernell Whitaker of Norfolk, Va., won berths today on the United States Olympic boxing team. Ricky Womack of Detroit, like Biggs and Whitaker a world amateur champion, did not. This was the second and final day of the Olympic Box-Offs at the Caesars Palace Sports Pavilion. Six fighters qualified Friday night and the final six made it today. As many as 6 of the 12 will be favored to win gold medals in the Los Angeles Olympics, which begin three weeks from today.

HOME buyers often worry that a blot on their credit history could result in the denial of mortgage financing, even if they are not the type of person who intentionally allows bills to pile up. Horror stories abound about people who suddenly discover major problems on their credit records without ever having suspected anything. ''Sometimes it's as simple as having moved and never receiving the forwarded bills in the mail,'' said Maryann O'Hara, a senior mortgage-origination officer at Mechanics & Farmers Bank of Bridgeport, Conn. But if a loan application has been rejected, whether because of a troubled credit history or insufficient resources, financial counselors say the rejection should never be viewed as the last word.

PASSING muster with the board of directors of a cooperative apartment has grown tougher for buyers over the last five years, according to leading sales agents in the city. The agents report that the boards, particularly in established Manhattan cooperatives, increasingly want more detailed personal and financial information from buyers. The review process also is taking longer and costing the buyer more. It is mainly the result of the rise in the prices of cooperatives, the sales people say. High prices and large buyer mortgages have generated more concern over buyers' ability to avoid default. The boards also appear to be looking more closely for signs of uncooperative attitudes that may carry over into uncooperative behavior as a resident.

An Amtrak passenger train with 278 people aboard derailed while crossing a washed-out culvert this morning, killing at least three people, injuring more than a hundred and trapping passengers in a crushed sleeping car. The train was bound from Washington to Montreal. Officials said tonight that two people were believed to be still inside the sleeping car, which overturned in a shallow pool of water. Rescue workers using blowtorches and a crane continued searching for survivors late into the night. Eighty-eight people were taken to the Medical Center Hospital in Burlington; 57 others were taken to the Fanny Allen Hospital in Winooski. About 140 people who were unhurt or suffered only slight injuries were taken by bus to the Williston Armory. Most of the injured were treated and released.