Those far-sighted gardeners who started their lettuce, potato and brassica seedlings right on time in January are facing the dilemma of figuring out, given an unusually benign spring, if they should go ahead and put them into the garden now. The seedlings are ready to go out, but who knows if we'll suddenly be hit with a snowstorm or severe freeze?

Under normal circumstances, it's safe to plant cool-weather seedlings starting the first week of April. The last frost in this area occurs between April 10 and May 10. Not that you have to worry too much about a light frost with cool-weather crops; they're quite hardy. But a hard frost, which can occur in the next couple of weeks, can do a bit of damage.

Ideally, the gangly seedlings should be hardened off in a cold frame. At this point, they can be moved temporarily into the cold frame round the clock, in preparation for their ultimate repose in the garden. The cold frame will protect tender seedlings from any harmful weather that may unexpectedly occur.

If no cold frame is available, the careful gardener will keep the plants outside at least during the day, and if the weather report indicates mild overnight temperatures, they won't have to be brought in at night. They should be protected at all times from wind and rain -- a well-protected, south-facing porch works well; a deep box under an overhang will do as an alternative. The sides of the box should be tall enough to give the young plants plenty of windbreak. A screen or an old storm window to cover the box will keep cats and curious children from bothering the plants.

After a week of this hardening off, it should be safe to put the seedlings into the garden by next weekend, as long as you're prepared to give them some protection in the event of severe weather. It doesn't have to be elaborate: Waxed-paper cones, which I've been using for years, are cheap and effective. Single sheets of newspaper draped over plants do equally well, although you may find the papers scattered all over the garden in the morning. More elaborately, clear plastic cloches, which also aren't very expensive, can be set up semi-permanently over seedlings to protect them and hasten their development. Once they push to the top of the dome-shaped cloche, remove the structure and use it for your next crop of seedlings. POTATOES traditionally go in on St. Patrick's Day. If you didn't get them in then, don't despair. There's still plenty of time for an early (August) crop. Buy seed potatoes by the pound, choosing, if you can, large tubers with plenty of eyes -- those tiny white-tipped nodules that will sprout and grow once planted. Cut the potatoes into chunks, one to two inches across, making sure you get at least one eye on each piece. Dig trenches two feet apart and eight inches deep, and scatter the potato pieces in the trenches every four inches or so. Cover the potatoes with straw or mixed mulch, such as straw and leaves. You can also use dirt, of course, but if you use mulch only, they'll be a lot easier to find at digging- up time if all you have to do is push aside straw or leaves rather than soil. You'll be able to begin harvesting tiny new potatoes in late May or early June, and fully mature potatoes will be ready in August when the vines have all died down. You can plant another crop of potatoes in early August for a fall harvest. Potatoes harvested late in the fall keep better over winter months. TRANSPLANT -- Lettuce, broccoli, cauliflower, cabbage, Brussels sprouts, leeks, onions. PLANT -- Beets, carrots, turnips, rutabagas, potatoes, radishes, spinach, lettuce, asparagus, rhubarb, strawberries, peas, clematis, roses, peonies. START SEEDLINGS INDOORS -- Tomatoes, peppers, eggplant, celery, summer squash, cucumbers, melons.