By now, of course, all diligent gardeners have tilled or plowed their plots, pulled early weeds, added fertilizer and lime and generally prepared their soil thoroughly for spring planting.

Right? Well, maybe not.

If, like me, you're among the many gardeners who let Easter sneak up on them and awaken one morning to a full-blown spring and a deep sense of panic, don't despair. Hereabouts, untold events are possible in the garden.

We have many gardening seasons and the opportunity for many gardens within a year. All that you'll lose by missing out on an early-spring garden is a little face with fellow gardeners. So don't give up on planting, just forge ahead. I've said it before, and I'll say it again: I've successfully planted peas as late as late April. You can't expect as much of a yield, of course, but you don't have to miss out on fresh peas just because they haven't come up yet. Besides, there's always the fall. The same goes for a lot of other early, cool-weather crops.

Now is the time to be putting in broccoli, cabbage, lettuce, cauliflower and Brussels sprouts seedlings. When you get your plantpacks home from the store, or if you've already got your own started and hardened off by now, give them a good soaking and let them drain.

Dig a narrow, fairly deep hole in your garden. You want to plant the seedlings far enough into the soil so that only the top leaves are above the ground. The stem should be completely underground to give the tender seedling vigor and prevent it from breaking if it's whipped by stiff winds.

Don't side-dress your seedlings with mulch or compost until they've had a chance to establish themselves. Within a week or slightly more, you'll notice new leaves growing; so it will go for the next month. I like to side-dress brassicas two or three times during growing season to keep their roots cool and give them nourishment to produce larger heads and better yield.

Onion, garlic and leek seedlings get slightly different treatment. Rather than burying them deep, place them only two inches down, so that half their spindly growth is below the soil level and half above. I've found that onion-family members, if planted in reasonably good garden soil, rarely need to be side-dressed later.

Members of the onion family can be planted fairly close together; I allow six inches between seedlings. Broccoli and other brassicas, however, need lots of space if you want top yields. Side dressings of manure or compost ensure large plants. But if you plant them much closer together than 21/2 feet, they suffer in close company. Mature broccoli plants can have foliage two feet across, and each plant should be allowed plenty of air circulation. It may seem like a lot of space to give them, but it pays off handsomely later when you see your small seedlings grow into large plants to fill the generous space you've allotted. Lettuce will stand closer company -- spacing of six to eight inches is plenty.

In any case, the comforting message in all this is: don't panic. All these cool-weather vegetables can go in, as seedlings, anytime up until mid-May. Meantime, keep up with plantings of root crops and successive seedings of lettuce. Carrots, beets and radishes are plantable and can be harvested virtually 10 months of the year hereabouts. Only the hottest weather will stump them. RISKY BEANS -- If you're abreast of your gardening chores, you may want to chance sowing green beans now. If you do, don't overdo, because you may lose the whole crop, since it's a little early. But if, like me, you're a lover of tender tiny green beans, it's worth sowing half a pound of the bush or pole varieties just to get a jump on the normal season, despite the risk of frost. The earlier I get them in, the less trouble I have with bean beetles. SPRING IS HERE BEDDING-PLANT SALE -- At the corner of Washington Boulevard and North Glebe Road in Arlington this Saturday. Choose from a variety of bedding plants on display from 9 to 6. Sponsored by the Arlington Metropolitan Chorus and Arlington Dance Theater. 558-2165. PLANT WORKSHOP -- Learn how to grow plants from cuttings and seeds at a two-session workshop at the Northern Virginia Community College this Saturday and April 30 from 9 to noon. Cost is $20 and enrollment is limited. 323-4551. SPRING BLOOMS -- Brookside Garden's annual spring-flower displan is in full bloom now through April in the Conservatory. Open 9 to 5 7889aily and till 9 this Friday at 1500 Glenallan Avenue, Wheaton. Free. 949-8230..