Men's fashions are due for a minor revolution, to judge from the fourday panorama of shows just concluded here.

Menswear has always been divided into two parts: the avantgarde, rarefied and expensive designs for a small audience -- and the rest, which most people wear. And this year, the big volume houses are wondering how far they can go in adapting the new padded shoulders and slimmer shapes for the man on the street.

That was only one topic of discussion through the weekend as men's fashions for spring were modeled, discussed and turned inside out at the Menswear Fashion Association conference here. The gathering of designers, retailers, manufacturers and the press was sponsored by the MFA -- the promotional arm of the huge American menswear business, with a yearly retail volume of $26 million, including textiles, shoes and accessories.

It comes at a time of transition and speculation. Washington stores are still clearing out their men's clothes from the fall season, and the spring items are just being shipped into specialty and department stores. Menswear designers in New York are currently presenting their line for the fall of 1979.

And amid it all, the volume manufacturers are asking themselves how quickly their diluted versions of the big-shouldered, tapered-waist clothes -- reminiscent of Cary Grant in the 1940s -- will be accepted by the public.

"It's already beginning to sell," says Philip Miller, president of Neiman-Marcus, "because it's all-around a more gentlemanly silhouette and away from exaggeration. It should be easily accepted by Washington."

And Bob Connors of Hart, Schaffner & Marx, one of the largest menswear manufacturers, says that "We'll probably have padding in some of our suits by next fall too -- and maybe even more later, if that's what the customer wants." But certainly no exaggerated Joan Crawford shapes, he says.

The Washington man looking for purchases that will stand him in good stead for a while can expect to find:

Jacket lapels no wider than 3 1/2 inches. (By next fall, lapel widths will be down to 3 inches.)

Thies 2 1/2 to 3 inches wide, essential with the new narrow lapels and tiny collar shirts. In general, everything is getting skinny together, even the belts.

Pants cut straight from the 20-inch knee to the ankle, or tapered an inch or two and cuffed -- if there's enough fabric to do it.

Single-vented or ventless jackets (the latter is thought better for the man with a broad rear, since the single vent tends to pull open.)

Shirts with tiny collars and tiny patterns -- and less fitted. For leisure, the boxy bowling shirt or occasional Western detailing.

Two-piece suits displacing the three-piece variety, with single-button styles getting a little competition from double-breasted suits. For both single- and double-breasted suits, the fit is very relaxed, and buttons are placed a little lower, for low-slung effect.

Softer construction in lined or unlined jackets, for a more comfortable fit.

Natural fabrics (when you can afford it), or natural blends in earth colors, including the beiges, from sand and mushroom to sage and mossgreen. Textured fabrics like summer tweeds extured fabrics like summer tweeds extend the wearing season through early fall.

Leading the pack with the best of the new shapes are Bill Kaiserman for Rafael, Calvin Klein, Lee Wright, Ralph Lauren, Sal Cesarani and David Shapiro for Ursel. But they will hardly be the only game in town. With retailers and consumers both reluctant to make their clothing obsolete, the styles that have been popular for the past couple of years will be an option also.

If the new clothes don't match the formula set by John Molloy in his popular "Dress for Success," it's intentional. Chip Tolbert, fashion director of MFA, compares simplistic success-dressing formulas with "fashion cloning." He says, "It's making U. S. businessmen look dull and drab like they're being xeroxed into their clothes each morning."

According to Tolbert, the Molloy book is full of myths about menswear -- like the statement that light colors won't succeed at the executive level, despite regional and climate differences, or his claim that some colors generate a Pavlovian response (Molloy says a Mexican-American won't buy anything from a salesman wearing anything red). Tolbert also doesn't understand Molloy's reasoning that high fashion is necessarily bad, since the same high-level executives are expected to keep the other aspects of their lives as current as their incomes will allow.

Among the non-business-suit options for spring are: silk shirt-and-trousers combinations -- as an alternative to tuxedos in all black or all white; the cotton sweater, loosely knit and often V-neck or boat neck as an alternative to T-shirts; terrycloth pullovers and jackets; and as in women's fashions, oversized tops with skinny pants and shorts; and funny conversation pins for the lapel.

Washington may have a reputation for being conservative, but the new styles may suit local merchants well.

"We've had a terrific response to the narrower proportions through the fall and this encouraged us," said Britches co-owner David Pensky, who says that the average width for both their collars and their ties for spring will be 2 3/4 inches, both down from last spring.

Raleighs completely sold out of their fall Calvin Klein furnishings and did very well with his suits and jackets -- all with narrower proportions. "It was an excellent collection for us," says vice president for men's clothing Jules Avola. "We've taken a bigger position on his line for spring and have just placed an even bigger order for next fall."

"The look has laready done very well for us," says Jacq Staubs of Woodward/Lothrop. "And I think even the more conservative Washington man has begun responding to the narrower proportions."

Still, some Washingtonians may demur. "It's bound to affect the mature man least of all," concedes Neiman-Marcus' Miller. "Because more than anything else, he looks for consistency."