He wears a gangster-striped suit, pale blue socks, brown suede shoes and a yellow mum poked through the buttonhole of his lapel.

He says such things as "draped clothing for men" and "corridor of menswear sensibility" and "elegance through softness." Can this man be serious about fashion?

"He'll influence the way many men in Washington are going to dress," said David Pensky, an owner of Britches of Georgetowne. Britches has promoted only three designers in 17 years in business: Ralph Lauren, Alexander Julian and now Alan Flusser.

Pensky sees the future in Flusser. "He shows a way of dressing and an esthetic sense that seems very right for Washington and for now."

Flusser is the man in the double-track pinstripe, double-breasted suit with a 1937 Esquire tucked under his arm. Once he was the spiffiest dresser on the teen-age golf circuit in New Jersey, later a designer for Pierre Cardin menswear and now designer of the Alan Flusser collection. He's also author of "Making the Man," which tells how to buy and wear the clothes he makes. (He's at Britches in Georgetown today signing the book.)

Flusser was out at the Britches warehouse in Alexandria yesterday to meet store managers and sales people and explain why his clothes buckle a bit around the armhole and drape in the trousers.

"These clothes have a fullness in the chest and back that allow for freedom of movement," said the designer, taking three big strides at the front of the room to demonstrate the "drape" cut to the attentive, pleated-trouser crowd.

Flusser admitted that the clothes may seem to add 10 pounds across the chest, but what is lost in a slim appearance is gained in comfort and ease. Besides, he is quick to point out, that silhouette didn't seem to bother such drape suit aficionados as the duke of Windsor, Douglas Fairbanks Jr. and Fred Astaire. In fact, Flusser's designs are more commercial models of his own suits, which he has custom-made at Anderson & Sheppard on Savile Row in London--tailor to the duke, Fairbanks and others. "Fred Astaire's suits were so comfortable he probably could have danced in them," teased Flusser.

Easy-cut, comfortable suits for men are part of the American tradition of Brooks Brothers clothing. But while the Flusser suits are roomy, they are also shaped with broadened shoulders and an indented waistline, which, according to Flusser, "may make the chest look heavier, but takes off pounds at the waist."

They are not nearly as shapely as the European cuts of Yves Saint Laurent, Cardin and others whose skinny, tapered fit caught on in the late 1960s. "Those suits were so stiff that the man took on the shape of the clothes," said Flusser.

Flusser is convinced that the man who feels cramped in a fitted suit is ready for a change. "Some suits pinch so much men can't wait to get home to change," Flusser said. "The function of clothing is more than having it look right when you stand still in front of a mirror." Flusser can sit comfortably in his suit without opening his jacket.

Flusser is hooked on function. He passes up center vents because he thinks double vents work better when a man puts his hand in his pocket. The buttonhole on his lapel is open to accommodate a flower (and there is a loop behind the lapel to hold the stem in place). The four buttons (never three) on the sleeves are so close "they kiss," an old English tailoring tradition, says Flusser. And those buttons unbutton for those who want to roll up their sleeves, or simply prove that their buttons unbutton.

Last week, on his way to an IRS office, Flusser made his usual stop for a boutonniere at his neighborhood florist in Manhattan. He was wearing his boldly pinstriped suit. "I think it looks a little gangsterish for the IRS," warned the friendly florist. Flusser went home to change. His tax agent might not have heard about the duke of Windsor and the drape cut suit.