Dresses; Pick a dress, add a lightweight coat and accessories, and you're off and running - starting the day with efficient dispatch

THE advantages in having a closetful of dresses instead of a collection of skirts, jackets, and blouses are beginning to dawn on the American woman. There's the timesaving aspect. Reaching for a dress in the morning is a one-stop decision, vs. the two- or three-stop operation of assembling a combination of separate pieces.

You eliminate the shilly-shallying over which shapes, colors, and textures mate with which. You pick your dress, add your lightweight coat, if necessary, and your accessories, and you're off and running, pleased to start the day with such efficient dispatch.

The economics of acquiring a dress instead of a separates turnout are also persuasive. As Sy Buvitt, of the Evan-Picone dress division, has pointed out, ''With a dress, a woman buys an entire outfit for $140. A sportswear outfit at the same quality level would run $250 and up.''

But which dress is the question. The way the assortment is growing, customers will find plenty of choices in the stores this spring.

The big winner is the chemise, which, although it never really went away, has been given a new lease on its fashion life since Yves Saint Laurent starred it in his fall collections. Much less shapeless than in its earliest form - the 1950s Balenciaga sack dress - the waistless chemise has many variations. They extend from the inexpensive cotton knit that is an elongation of the basic T-shirt on to couture-class designer numbers of costly workmanship and luxurious fabric.

Even the low-torso dress with the skirt that fans out in pleats or gathers below the hips is a kind of chemise. What sets this season's chemise apart from previous interpretations of the style is width across the shoulders and a narrowing down toward the hemline. Some chemises are built along the lines of the kimono.

Then there is what might be called the MBA dress, a white-collared variation of the shirtmaker that appeals to executive women, both junior and senior types. Usually worn with the businesswoman's favorite floppy bow tie, it has a well-defined waist and comes in silky foulard solids as well as patterns.

Another workingwoman's standby, the coat dress, is equally popular. The new double- and single-breasted versions in linen look especially right for the office. The simple sheath that buttons down the back is a good 9-to-5 choice, particularly the cap-sleeved warm-weather versions. Big patch pockets are the latest touch, and they are placed low on the sides.

Pinafores layered over a plain dress - an idea explored by Kasper - offer a change of looks, as the pinafore can be removed at the end of the day when the underdress, plus some festive jewelry, goes out for the evening.

Stripes, plaids, and polka dots are the leading prints, but bold graphics are not lacking. Albert and Pearl Nipon have a group of dresses in a modern Miro pattern of red, black, and white, as well as a series in tiger-striped silk. The dramatic art-inspired print is also proposed by Oscar de la Renta. His patterned silks have riotous arabesques of color, strengthened by black on a white background, making what you might say is a strong print statement.