Overture Note: Like a lot of people, Gilbert Kaplan dreamed of conducting a symphony orchestra through one of his favorite pieces of music. Unlike a lot of people, Kaplan, the multimillionaire publisher of Institutional Investor, has the means to make his dream come true. Recently he hired the American Symphony at a reported cost of $100,000 and led them through Gustav Mahler's Symphony No. 2, "The Resurrection," at Avery Fisher Hall. The musicians were so impressed that they have asked him to lead them again at a benefit marking the symphony's 20th anniversary next April in Carnegie Hall . . .

* London Theater (or Theatre), Act One Note: Tom Stoppard's most recent opus, "The Real Thing," a play about middle-class adultery opened in London recently. Puns are a part of it but, much to the distress of the Observer's critic, Robert Cushman, it is too much like other people's plays. "Why does he mess around with drawing-room naturalism?" Cushman lamented in print. The lead is played by Roger Rees, who had a limited engagement of celebrity in New York last year playing the title character in "Nicholas Nickleby" . . .

* London Theater (or Theatre), Act Two Note: Peter O'Toole brought his production of Shaw's "Man and Superman," in which he plays Jack Tanner, to the West End and elicited a three-paragraph review from Sunday Times critic James Fenton, who parodied the star by writing a lush's "sh" every time the letter "s" was called for. Wrote Fenton: O'Toole "should rush on to shtage and, again preferably, he should come to a halt before he fallsh into the auditorium. Thish Mr. O'Toole pulled off shplendidly. After that, it ish shout, shout, shout all the way" . . .