May 12, 1985

Take the incumbent Mayor's political autobiography and turn it into a musical revue? People who ought to know about such things told Charles Strouse that it was a crazy idea. Whether they were right or not, ''Mayor'' is already An Event - even before tomorrow's opening. Such premature celebrity leaves the show's creators and producers more than a little anxious. It also delights the man who plays the title role in real life, as he imagines voters humming mayoral tunes all the way to their polling places in September. As the show was going through frantic early-morning and late-night revisions recently, the Mayor and the people who are putting ''Mayor'' on stage retraced the path to the Top of the Gate at 160 Bleecker Street and tried to assess how the musical would be received.

TWO years ago, a little-known American cosmetics company called Cosmair quietly began buying up the supply of customized aerosol cans in Europe, where they were used to package a break-through hair styling foam called mousse. It was a product that had not yet reached America's shores and when Cosmair introduced its Free Hold mousse here six months later, its can strategy paid off: Cosmair got a running start in the market, preventing rivals from posing a challenge for several months until the can supply could be replenished. By then, American consumers were already equating Free Hold with mousse. And although competitors quickly started selling their own products, Cosmair has kept its commanding lead, now controlling about 40 percent of the lucrative $150 million American mousse market. It far outpaces the rivals that patterned their own products on the mousse developed by L'Oreal, one of Cosmair's European owners. Cosmair's aggressiveness in shaping the mousse market, and its move last year past the venerable Estee Lauder into the No. 3 spot in America's $7 billion cosmetics and fragrance industry, has confirmed for analysts and competitors that Cosmair is a force to be reckoned with. Until recently, the products of this privately held company - which include Lancome and L'Oreal cosmetics, as well as Vanderbilt, Chaps and Lauren fragrances - have been better known than its corporate name.

WITH only four pitchers on his squad of 12, Dick Raposa, the head baseball coach at Tunxis Community College in Farmington, needs a pitcher who can do double-duty. Oddly enough, he has one in Kenny Rodriguez, a stylish left-hander who is also a stylish right-hander. Those steeped in baseball lore can go back to the 1940's for a parallel, to Ed Head, a right-handed pitcher for the Brooklyn Dodgers who occasionally threw with his left hand. Mr. Rodriguez, by being able to pitch with either arm, gives the Tunxis team another pitcher. Indeed, Mr. Rodriguez has, at times, pitched most of a doubleheader without putting undue strain on either arm.

Until now Hartz Mountain Industries, the New Jersey-based company that rose to prominence as a manufacturer of birdseed and pet food, has focused most of its real-estate development efforts in the Meadowlands. But with the construction of a 24-story office tower on Madison Avenue at 61st Street, the company is making its developement debut in Manhattan.

The fruits of gentrification in two Brooklyn neighborhoods will be on display next Sunday in house tours of the Park Slope and Fort Greene sections of the borough. In Fort Greene, a neighborhood that in the past has been associated with high crime and rundown housing, tour participants will see carriage houses, cottages and cast-iron buildings, as well as the turn-of-the-century brownstones and row houses for which the area is best known.