A Matter of Proportion If a man knows how to look good in a navy-blue suit, a white shirt and a dark tie, he can wear almost anything, says menswear designer Alan Flusser. "If a man knows the fundamentals of how to dress, if he's got every proportion down right including the relationship between the width of the lapel, the tie and the collar, then the whole world of pattern and color is open to him. And a mistake in color may make him look a bit eccentric, but not wrong," says the Coty Award-winning designer.

His second book, "Clothes and the Man" (Villard Books, $29.95), deals with these basic principles. And on a radio talk show this week Flusser was answering questions about men's clothes.

Callers sought out basic information, he says. One asked how long trousers should be. "They should sit on top of the shoe with a little break over the instep," Flusser advised. Another wanted to know about the width of pants legs. "They should be proportionate to the man's body," said Flusser. Quite specifically, they should be no wider (or narrower) than three-fourths the length of the shoe.

About cuffs? "It's up to the wearer to decide to wear them or not." But cuffs should be straight, not angled like uncuffed pants. According to Flusser, a man under 5 feet 10 should wear cuffs 1 5/8 inches wide. A man over 5 feet 10 should wear his cuffs 1 3/4 inches wide. "Those are the same rules the tailors use on Savile Row," he added.

Flusser, who sells his clothes primarily through his own New York shop and J.C. Penney (and whose clothes sell from $27.50 for one of his shirts at Penney's to $227.50 for a silk and cashmere shirt in his own shop), considers Fred Astaire representative of the style he most admires. "He epitomizes studied nonchalance," says Flusser, who adds that "Astaire style" influenced him even as a child, since Flusser's father was taken with the way Astaire dressed.

"Astaire dressed in a very personal, understated way. He knew how to wear clothes for his physique. He wore short jackets and wore pants a little fuller, partly to give him room to dance, but also because with shorter jackets one needs to wear fuller pants." Flusser suggests short people should follow that proportion.

"No one wore clothes better than Astaire. He looked like he was moving when he was standing still. He had oodles of style."

Flusser likes the idea of dressing such customers as Bill Blass, Bobby Short, Bill Cosby and Tom Wolfe through his own shop, but also reaching the general public through Penney's. "They've given me the opportunity to influence the taste level of a mass amount of people."