SPRING'S A LITTLE late this year, a bashful beauty tantalizing an audience eager to glimpse her charms after the unremitting winter. This year we missed the normal false harbingers: no January thaw; no mid-February crocus foolishly blooming; no defiant nubbin of rhubarb peeking for a sun that flees to an early bedtime.

Winter set its chill deep and allowed no unseasonable flights of fancy. But the change of seasons is inexorable and undeniable, governed by light - the length of day and night - not the vagaries of weather, and spring IS arriving. The signs are as the calendar that says on March 20 day will be as long as night. Equinox.

The other sure signs are more fun to observe than marking the calendar: Willows fuzzying green, maples and sumac fuzzying pale red; honeysuckle leaves doing what most leaves did last fall - darkening, crisping, falling to make way for new growth.

Bird know Cardinals grow amorous, and the males who have chased their mates-for-life away from choice seeds all winter now shuck seeds and feed them beak-to-beak to basking females. Juncoes, the aloof and busily-feeding snowbirds of winter, suddenly turn agressive swirling in groups, establishing pecking orders for communal treks north. Goldfinches regain gold from their winter drab. The tentative "feeble-feeble-feeble" of the tufted titmouse of December/January is now a piercing "PETER-PETER-PETER."

The first migrant to these parts - the fox sparrow - is overdue. He'll momentarily appear, scratching aside last fall's leaves in search of the first grubs of the new season. This fat, rusty fellow, the biggest of the sparrows, can survive with no trouble even if he rushes things and the grubs are still frozen in solid - he is really of a seed-eater family. But his enthusiams is for bugs, and it's contagious. Soon after the fox's arrival, the seed-eaters that were here all winter are scratching away with his two-footed determination - towhee, white-throat, purple finch, even cardinal.

On the heels of the fox sparrow come redwing blackbirds and grackles. Horned owls that hatched over a month ago are working up to fledging.

All these signs send the gardener to serious study of the seed catalogs and the naturalist to serious study of buds. Sap is flowing and what is imminent is the full rite of spring - the bursting of buds, the flowering, the greening. After all, that March 20 date is called the Vernal Equinox.

But this miniseason now upon us, this prevernal time, is more than a time of anticipation, an appetizer. It has some hors d'oeuvres that are meals in themselves, and they are worth seeking out.

They are wildflowers of a group that is not a group to the professional botanist, for their 10 to 12 species come from widely differing horticultural families. But they group for the amateur, the naturalist eager enough to get out and reach out for spring. In this area, the reaching is easy - Rock Creek Park or any of thousands of areas that has a relatively undistrubed setting under large deciduous trees - oak, poplar, beech, hickory - so common here.

Some call these wildflowers prevernals; a more romantic name is spring ephemerals. They lead their entire lives each season in the short time between the end of the last hard freeze and the beginning of when the big trees leaf out and shut off their sunlight.

Their life cycle leaves no margin for error at either end. If they wait too late they lose their vital time in the sun to the trees' canopy above; if they spring too soon a frost fells them or clamps off early-season insects on which they depend for pollination. In a tiny span they do their whole bit for the year they send up foliage through the bed on the forest floor, they gather a full year's supply of energy from the sun and store it in a bulb or tuber, and they flower, complete their sex lives and make their seeds.

Their two-or three-week life span is furiously spent harvesting the sun, since no sustenance is available in the unawakened earth. When the sun is blocked off by new leaves on the trees they die back to soil level.

With the possible exception of the Pacific Northwest, this is the best area of the nation for prevernals. There are four quite common and a fifth just behind.

Erythronium americanum. It's known as dogtooth violet, adder's tongue and trout lily, the last because some say its bloom signals when brooke trout begin to bite. It gets at most six inches tall, with a single flower rising mauve with yellow undersides on the blossom. Leaves are tulip-like with the green blotched with tan.

Corydalis aurea, actually a family that includes two members: To the east of here that little clutch of fern foliage and white and yellow flowers is likely to be squirrel corn; to the west, Dutchman's breeches. Their special charm is the blossom, with its inflation of joined petals, which gives it the Dutchman's breeches name. The white forms, often four to six of them on a golden pestule, light up and glow if held the right angle to the sun. They are mostly found on slopes.

Anemone quinquefolia, the wood anemone, is best found in early afternoon since it blooms fully only for full sun. Tiny, hard to find, but not really rare. Rosy-purplish blossoms never opening (it has no petals, only buds - sepals), mostly found in wet areas.

Claytonia virginica, often called spring beauty. A tuber with new blooms each day ranging from white to bright pink, opening from a fiddle-head of buds. The outdoorsman Euell Gibbons rated its roots high on his list of wild foods ("little potatoes") and suggested the beds benefits by thinning and the plants are transplantable to suitable environments.

Dentaria laciniata, commonly toothwort. Bell-like blossoms off elongated violet-type leaves. Blossoms usually white, but pink to lavendar happen. Sometimes the plant will climb a foot or two up a rough-barked tree.

There are other wildflowers that will confuse the woods-wanderer in early spring - bloodroot, the assorted hepaticas and trilliums, May apple jack-in-the-pulpit, windflower - but they are not the strictly prevernal, they go on after the leaves are overhead. Searching for any of these prespring plants get you into the woods, park or vacant lot when life at its very essence is renewing.