July 1, 1984

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.''