It doesn't seem all that long ago that women would not venture out of the door without hat or gloves. And not just any hat or gloves. The hat, in fact, was usually sold with a directive from the saleslady on the precise angle it should be worn.

Exit the period of compulsive hat-wearers.Enter the time of hats for the fun of it.

Summer in the tropics (Washington) has always, of course, given hats a boost. And they're popular poolside or oceanside to protect face and hair, as well as to camouflage an errant hairdo.

But young women who have never worn hats before are now grabbing them for office glamour, as well as for the beach. There's a wide range of basic -- and affordable -- straw hats available. And wearing a hat guarantees a turning of heads.

But if you're looking for more ideas on head coverings of all types -- and a wealth of information -- The Hat Book , by Alan Couldridge (Prentice-Hall, Inc., $8.95), is a heady place to start.

The author (English, of course, and one of that country's top millinery designers) clearly defines the terminology and reviews all aspects of head lore: from patterns, to blocking of straw and felts, to the wrapping of turbans. And his range of bridal headdresses has to touch on every possible whimsy that could occur to a bride, plus some traditional ideas that might have been overlooked.

Couldridge also has come up with a remarkable list of ideas for decorating hats, along with explicit instructions and his own fanciful drawings. (His book provides not ony a complete and amusing study of hats, but a splendid guide to fashion illustration: Couldridge is a tutor at London's Royal College of Art Fashion School and a designer for Liberty & Co.)

Instead of poking bunches of flowers through a straw hat, Couldridge suggests stitching the posies onto a ribbon and then anchoring the whole thing.

As an alternative to the usual ribbons, he suggests braids, as many as three or four stitched around a headband, to complement tailored linens. He is, in short, for using virtually any fabric to band a straw hat, first stiffening the edges to prevent fraying or fraying them intentionally for effect. Appliqued lace, from ribbons or even cut from the edge of an old curtain or tablecloth, for example, might be used to decorate the base of the crown, or cut apart and used as appliques alone, or combined with ribbon.

Among some of Couldridge's other surprise hat-trim ideas:

A schoolboy's elasticized belt from the five and dime.

Veiling, scrunched up, draped and gathered fr a Mata Hari effect.

String, in various textures and widths, including the post-office variety, for nubby detail, particularly on natural straw.

A strip of metal, plastic, or even leather for contrast.

Ink drawings or fabric paint designs. ("Remember," warns Couldridge, "that the design will 'bleed' because (real)straw is very absorbent, so it is important to calculate for this in the pattern you decide to use.")

Studs, on the crown (so the claws don't show under the brim), or on a separate headband, to prevent damage to the hat itself.

Embroidery silks on straw.

Another idea, not mentioned by Couldridge, but in keeping with the current high-gloss trend in fashion: metallic decorations, such as a bronze leather band or gold-threaded yarn or ribbon.