What was going on when I was born?

Set among some of the city's most frequented hotels and sought- after apartments on Central Park South is a building that is perhaps best known for the restaurant that occupies its top floor, the Nirvana. But there is another aspect of the 15-floor structure at 30 Central Park South, between Fifth Avenue and the Avenue of the Americas, that sets it apart from such neighboring properties overlooking the park as the Plaza Hotel to the east and the Park Lane and St. Moritz Hotels to the west.

Tourist Time The Fourth of July holiday weekend traditionally marks the beginning of the peak summer vacation season, and this should be a strong summer for the tourist industry. The much-improved economy, the Olympics in Los Angeles and the World's Fair in New Orleans will boost tourist traffic nationwide by about 5 percent this summer, says Saul F. Leonard, national partner in charge of leisure time and gaming industries at the accounting firm of Laventhol & Horwath. Not only will there be more tourists, he predicts, but they will be ''spending more money on their vacations this year because the economy has improved so much.'' Because of the strength of the dollar, many Americans are likely to invade European vacation spots. The United States is not expecting many foreign visitors, however, because the strong dollar has made this country a relatively expensive spot to sojourn.

The slider, the pitch that at times made him invincible, again failed Ron Guidry today as he gave up three home runs and the Yankees lost, 6-2, to the Kansas City Royals. Even in this discouraging season, the loss was disturbing to the Yankees because it was a further indication that when all is going wrong, they cannot necessarily turn to Guidry. ''He has been everything for us for so long,'' said Don Baylor. ''We tend to take him for granted.''

Wimbledon reached its halfway mark today, with John McEnroe and Bill Scanlon poised for another episode in their stormy rivalry. The two, who acknowledge their dislike of each other, will meet on Monday, when 11 American men and 5 American women compete in the rounds of 16. McEnroe and Scanlon gained the fourth round by different routes, with the defending champion easing by Wally Masur of Australia, 6-0, 6-4, 6-3, and Scanlon, seeded 14th, winning when 16-year-old Boris Becker of West Germany had to retire with torn ligaments in his left ankle while trailing in the fourth set. ''It will be a very interesting match,'' Arthur Ashe, the American Davis Cup captain, said of McEnroe- Scanlon. ''This is one I'm dying to watch.''

Poor people - Mayor Fiorello H. La Guardia firmly believed - have just as good taste as rich ones and lack only the chance to indulge it. A major test of his premise was the New York City Opera, which opened its doors on Feb. 21, 1944 and will reopen them - for the 40th year - on Friday. This season begins with ''The Barber of Seville,'' but on that first of first nights the opera was ''Tosca.'' The firing squad guns didn't go off in the last act - leaving the audience to assume that Cavaradossi had died of a heart attack - but otherwise everyone seemed pleased. Olin Downes came back to The New York Times afterward and wrote a review praising the performance for its ''refreshing sincerity.''

WASHINGTON AS the Rev. Jesse Jackson flew home last week with 48 American and Cuban prisoners from Fidel Castro's prisons in tow, what should have been a moment of personal triumph was overwhelmed by a roiling political furor at home that threatened not only his standing in the Democratic Party but Walter F. Mondale's chances against President Reagan. Mr. Jackson's association with Louis Farra- khan, whom he once called a ''surrogate,'' had been a source of controversy and political tension throughout the Democratic Presidential primary campaign. But things got even worse when, in a radio broadcast last Sunday, the black Muslim leader called Judaism a ''gutter religion'' and the creation of Israel an ''outlaw act.'' Up until now, Mr. Farrakhan had been Mr. Jackson's concern. But with the latest development, which exploded three weeks before the Democratic National Convention in San Francisco, the Muslim leader became a major political problem for Mr. Mondale, who faces the task of healing divisions between Jews and the Jackson constituency.

GOVERNOR O'NEILL can still recall the day in 1940 that he first rode on the Merritt Parkway. ''We were going to the World's Fair, and one of the great wonders was this road,'' he said. To Mr. O'Neill, the tree-lined roadway that gently winds across Fairfield County from Greenwich to Stratford has always been symbolic of Connecticut. ''I recall driving back home from Texas in 1951,'' he said, ''how good it felt to get back onto the old Merritt Parkway. I knew I was home.''

An old, vacant five-story tenement at 44 West 46th Street, near the Avenue of the Americas at the edge of the Diamond District, has disappeared and will soon be replaced by a new small-business structure. The new four-story building will become the home in December of AAA Locksmiths, which is moving there after 15 years on West 45th Street and 30 years before that at three other locations in the area.

Mary A. Martin said she has wanted to start a career in real- estate for the past 10 years. ''But I've never had time,'' she said. ''The Senate takes up all my time.'' So, after 12 years in the General Assembly, Senator Martin, a Democrat from Groton, has decided not to run for re-election this fall. ''I feel I've given enough,'' said the legislator who spent two years in the House of Representatives and 10 years in the Senate. ''I think it's time to enjoy myself, my family, and to go into something new.''

It only took from February to June. In the first week of February 1914, Mack Sennett released a very short film - just half a reel long - in which his new and as yet unknown comedian, Charlie Chaplin, mingled freely with the crowds who had come to see the annual ''Kid Auto Races'' at Venice, Calif. The auto races were real, though of course the children's peanut-sized cars had to roll down a fairly steep ramp in order to pick up enough momentum to stir any dust along the track. Sennett especially liked sending his clowns and a camera to public exhibitions of this sort because it gave him an event to photograph and a flock of free extras to fill in the sidelines. Chaplin had put together his so-called ''tramp'' costume for the very first time that day, and you will be able to see it newly hatched - mustache, derby, flexible cane but not yet the shabby shoes - during the massive retrospective of Chaplin films that begins its showings at the Public Theater on Tuesday.

The frequency of delays at the nation's airports is mounting, and Federal aviation officials say no quick solution to the congestion is in sight. Delays for the first four months of the year rose 55 percent from the corresponding period in 1983, according to the Federal Aviation Administration. The number of flights increased about 10 percent. Because the situation grew worse in May and June, delays through last Tuesday were up 75 percent from a year earlier, to a total of 183,000 affecting about four million flights. Unusually bad weather had much to do with the increase, the agency said.

INTIMATE MEMOIRS Including Marie-Jo's Book. By Georges Simenon. Translated by Harold J. Salemson. 815 pp. San Diego: A Helen and Kurt Wolff Book/ Harcourt Brace Jovanovich. $22.95 AT 81, Georges Simenon is the best-known living author and probably the richest. He has attained a celebrity greater than any fellow citizen since his native Belgium became an independent state. His work is sold in every French-speaking country and translated wherever the book trade exists. He began to write at 16, in his home town, Li ege, and stopped abruptly in Lausanne, Switzerland, at 69. Within that span, he wrote uncounted short fictions - he used to finish eight in a day - and 220 novels. Eighty-four of these have as their hero Inspector Maigret of the Paris police, whose fame has surpassed that of Sherlock Holmes. Like Sherlock Holmes, Maigret is perceived by addicted readers as a historical figure rather than a creature of fiction; many others see Simenon and Maigret as one.