Most men, and Washington men in particular, aren't quick to let go of a familiar suit or sportcoat they feel safe in.

For one thing, the big employer here, Uncle Sam, doesn't have much of a sense of humor about men stepping out of the suit-and-tie uniform in the office. And suits work well for most men anyway. The pockets are handy.

Besides, sexist but true, fashion-conscious men who keep up with style changes and admit it are still fairly rare.

So when fashion designers rev up for a new look in menswear, caution lights start blinking all over the place.

This is going to be one of those years. The old standbys will be back on the racks for those who insist, and many of the innovations will be gradual. But most Washington menswear stores and department stores are in a holding pattern on the more drastic changes, watching to see how they do in boutiques.

"I don't think the average male wants to look like he just stepped out of bed in his pajamas," grumbles one local retail executive.

What's causing the fuss?

Following the direction women's clothes have taken for the last two or three years, designers expect men to adopt a looser, freer, softer look in fashion this summer and to carry it over into fall. Changes include:

Jackets with less inner construction, the built-in features that give a garmet its shape. Instead, the clothes are supposed to take on the shape of the wearer and be comfortable, like a sweater.

Softer, more loosely woven natural fabrics that allow jacket sleeves to be pushed up and collars turned up to underscore a more casual, even rumpled look.

Cloths cut more loosely to replace the snug European fit that has been popular during the last few years.

Skinnier ties and shirt collars and narrower jacket lapels and pocket flaps.

Pants, often shaped with pleats and slightly tapered to the hem, meants to be cuffed for business and dress, uncuffed for casual wear.

Like many fashion trends here, this one started in Europe. The French call it decontracte, and both French and Italian designers have struck out for the style with a vengeance for fall. (In fact, Italian menswear designers have been directed to the look by an industry committee that hands out suggestions on fabrics and styles).

Stefano Ottina, an Italian who designs for Punch and has a shop at the Watergate, says, democate is the style of the moment because it is "deeply new."

"You feel liberated in these suits because they have no stiff construction."

but mainly it resulted from a search for "something that will make every man feel that what he owns is wrong and will want to change to something else," says Ottina candidly. He is already wearing his soft jacket, skinny tie and small-collar shirt.

American designers touting the look, including superstar Calvin Klein, refer to it as "unconstructed" and say they expect it to be worn for the office as well as for leisure.

But the Americans are far more cautious than their European colleagues (although there are plenty of suits with traditional construction around for business wear in Europe, too.) Even Klein, a "big believer" who showed his first menswear collection recently, ledged by offering his suits three ways: fully constructed, with some lining or totally unlined.

According to Klein, about 15 per cent of all his suits sold to stores so fare - 12,000 out of 80,000 - have no lining at all, or just a yoke at the back and lined sleeves "to make the jackets go on more easily." But Klein, who has built a huge reputation on correctly pegging his customers' tastes, is sure the unlined versions will sell first. "And even the lined ones are much softer than traditional suits," he said.

Some Italian suit makers expect to be able to sell their unconstructed jackets here at one-third less than the traditionally tailored one. But prices for the American versions, which require extra work to finish the seams, will often be up as much as one third.

"Most men are going to find it hard to understand that they must pay more for a jacket that has less to it," says Jack Schultz, a vice president of Bloomingdale's.

So what's a store to do?

Most big stores here are leery of the new style, which some consider "not refined enough" for the office in a city of office-workers.

For how they are banking on slightly looser-fitting jackets, narrower ties and smaller shirt collars to catch the not wildly experimental Washington customer. Narrow ties are already selling well in stores like Bloomingdale's where they have been in stock for a few weeks.

Boutiques, which expect big business in the decontracte look for fall, are starting slowly, too. "I don't plan to put all my eggs in one basket," says Alain Chetrit, owner of Silhouette in Georgetown. Ten percent of his stock for spring will be decontracte, but by fall it will be at least 25 percent. "By then, people in Washington will be used to the ample and unconstructed look of clothes, particularly the more ample jacket and sweaters," he says.

David Pensky, co-owner of Britches, will open a special store called "1359" (its address on Wisconsin Avenue) where the clothes will be mostly unstructured "except for some shoulder lining which will make the jackets easier to put on and take off."

Sid Mayer, vice president of Saks Fifth Avenue, which will introduce Calvin Klein menswear in New York this summer, says that his store has bought about 25 percent of the collection unconstructed, the rest constructed. But all of the unconstructed items are separate sports jackets. "I have to see it take hold in sportswear before I'll be convinced it will work in suits," says Mayer.

Raleigh's vice president, Jules Avola, who has seen both European and American versions of the unconstructed suit, has ruled it impractical for his Washington customers. He has tried some versions out with dry cleaners with disastrous results, he reports. "It comes out looking like something the dog has chewed."

The soft, loosely woven fabrics used by some designers aggravate the problem, according to Avola. "Fabrics like hopsacking have a natural tendency to stretch and now without the component to hold it together, it will begin to stretch just while hanging in stock."

At Brooks Brothers, where clothing never became as snug fitters as the European cut but was nipped in a bit for shaping, Stanley Jaffee swears he doesn't understand what the hoopla is all about.

"We've had unconstructed clothing for years," Jafee says, referring to the spring and summer suits in his Brooksaire line.

As for the new crop of decontracte styles, which Jaffee saw in France and Italy recently, "Customers don't want to look rumpled and messy," he says. "Life may be more casual but not sloppy."

According to Jaffee, Brooks has never stopped carrying a 2 7/8-width tie. "Everthing is moving back to us," he says.

Ralph Lauren, the man who, probably rightly, is often credited with introducing the wide tie in 1968, says he started wearing narrow ties several months ago. "There was such an overexaggeration of widness," says Lauren. "All of a sudden you start to see it so much, so commercially done, it has lost its elegance."

The new uncontructed styles, he predicts, will be overplayed and will peter out.

"It is bound to eventually go into a cheap look and end up in sports wear . . . it will be the new liesure suit."

And we all know what happened to that.