If you own a pair of classic gray trousers and another in black, you've got half your wardrobe organized for next fall.

That's a slight exaggeration, of course. But after three weeks of designer showings in Europe and more than a week in New York, it is clear that an easy kind of a look, typified by a long cashmere sweater over pants, is the way designers think women want to look next fall.

Ironically, the effort of the past year was to put women into snugly fitted clothes, wide belts and peplums. The about-face is a welcome change.

"Fitted clothes are hard to fit on customers," explained Bill Blass.

"These new clothes will fit everyone," said Calvin Klein.

Both designers were big promoters of the fitted styles.

Pants are not the only things the designers have in mind to capture consumer dollars next fall. Among their other ideas:

* Short flyaway jackets, often cropped above the waist and cut full in the back. Perry Ellis likes this look with high-rise skirts or pants. Geoffrey Beene often puts a flyaway jacket over dresses.

* Sweaters, rarely short and never tight-fitting. They glide over the body in a casual way. Such designers as Blass often replace the usual suit jacket with a sweater. Even when they are jeweled, as Oscar de la Renta or Blass do them for evening, sweaters are often teamed with casual pants or skirts that make the whole costume rather casual.

* The long pleated skirt as a fresh alternative to pants. While Beene and others stick with knee-length styles and some even shorter, the calf-length, stitched-down pleated skirt succeeds at Ralph Lauren, Ellis, Gloria Sachs and others.

* Cashmere, the key fabric for sweaters and other knits--and wovens, too. Ellis for the first time did some sweaters in cashmere, and Lauren interpreted both his coat dress and coats in cashmere.

* Gray, the pet color of designers in Europe and a favorite on Seventh Avenue as well. Black is still the strong, safe color for evening or day, and is often paired with white or strong shades such as royal or fuschia.

* Coats cut big in classic shapes to go over everything. Balmacaans, trenches, duffle coats and even pea jackets, all inflated in size to fit easily over suits and sweaters from this year or last.

* Sequins and embroidery and gold or silver threads to gussy up clothes for evening in contrast to the more casual styles for day.

* Bold, chunky jewelry on everything. Necklaces with big stones are piled on casual sweaters for day and add to the glitz for evening.

If it sounds as if you can dip into your closet and retrieve old styles instead of buying something new, be assured that designers are businessmen first, creators second. Nothing is quite as it was the last time around.

This fall's trousers, for example, are full at the top from pleating at the waist, but narrower and sometimes pegged at the ankle. Sweaters are longer, sometimes the length of tunics, and lean, often in a combination of colors and textures. Black and white continues a favorite color mix, but the new patterns are plaids (rather than dots or stripes) and animal prints, such as zebras or tigers. And while the coats are classic in shape and detail, they are cut with greater fullness and often in colors. When was the last time you saw an oversized shocking pink dufflecoat?

Even the big, bold jewelry shows up with a new twist, with fake diamonds like headlights in faceted glass. Gunmetal or black metal frames replace the traditional gold metal, and big, gloppy drop earrings are a must for evening. "Maybe all the casual clothes, as well as the dressy ones, need a heavy dose of jewelry to perk them up," said Kenneth Jay Lane, a master of junk jewelry whose pieces were used by every major designer for fall.

The more casual look has toppled the extremely high, spike heel. But the pump is still appropriate, and both the low and medium heel are often done in two colors rather than one. Designers also are casual about a price rise in clothes, which they anticipate at 5 percent for next fall. But Klein promises that "on some of the sweaters, we are able to lower our prices this year." Added to the fact that the clothes are more wearable than they have been in a while, that could be the best fashion news of the season.