That awful moment comes every time a man buys a new pair of trousers when, standing in front of the tailor's three-sided mirror, he must answer the inevitable question:

"Cuffs or plain bottoms, sir?"

Quickly you ask yourself, "Are cuffs "in' or 'out'?" You get no answer betcause you don't know. You look around. The tailor wears cuffs, the suit salesman doesn't. You wouldn't be seen dead in anything they have on anyway.

Sometimes the tailor will make a recommendation. You may accept it because he's in the clothing business and assume he's telling you what all the other men are doing.

Otherwise you end up making the same choice you've made for the past few years. Better play it safe one more time.

If you think your confusion makes you a fashion klutz, don't despair. The experts in the business are as undecided as you.

"Definitely cuffs," says David Barron, salesman at the trendy William Fox & Co. at Washington Circle. "Ninety percent of what we sell goes out with cuffs."

Plain bottoms, says Deborah Sonberg, salesman at Bloomingdale's men's clothing department at White Flint. Eighty percent of the pants Bloomingdale's sells are cuffless, according to tailor Anibal Morais.

"For trousers with a suit, we recommend a plain bottom," says Harvey Bobb of Raleighs Connecticut Avenue store. "We feel it's a style consistent with today and with the image in Washington."

At ever-traditional Brooks Brothers, it's cuffs that are "in" and always will be in. Manager Robert Bates finds them "dressier."

So does assistant manager Sharon Courtin of Britches of Georgetown. She says cuffs are neither "in" nor "out" this season. Cuffs sales are about 50-50 at the Wisconsin Avenue store.

"It's the customer's decision," says Georgetown University Shop manager Joseph Sewell. "We don't make recommendations."

"Absolutely optional," says Chip Tolbert, fashion director of the Men's Fashion Association of America, who wears cuffs himself because "I like them." In his travels for the New York trade association, the question he's asked most, he says, is "cuffs or plain bottoms?"

An informal survey of the office, the downtown lunch-hour crowd (and my own closet) indicated an overwhelming preference for cuffless pants. Most of the models in a recent issue of Gentlemen's Quarterly also go cuffless.

In the current spy thriller "Last Embrace," hero-agent Roy Scheider opts for plain bottoms. The villian who ends up dead chose cuffs.

Still, says Tolbert and his assistant John Simone, there appears to be a trend developing for cuffs, particularly with younger men.

"Cuffs is what they're showing in Europe now," agrees Carlton's manager-buyer Ralph Semsker.

From the experts:

Choose plain bottoms for sports pants, especially if you're wearing them golfing or workin in the yard. Cuffs are grass-collectors and debris-collectors.

Go cuffs for trousers of a light-weight fabric, especially in summer suits, because the trousers hang better. "You wouldn't hang drapes without weights," says Brooks Brothers salesman John Mingus.

Cuffs for the new pleated pants. They look better that way. On recommendation is cuffs 1 1/4 to 1 1/2 inches wide; another is the width of the waist-band.

Avoid cuffs with heavyweight fabrics such as tweed or corduroy. They're too bulky. They look bulky on flared pants, too.

Ask for plain bottoms for formal wear.

Do whatever you want. You're the one wearing the pants. CAPTION: Picture, no caption, by Gerald Martineau-The Washington Post