Now, new potatoes grown a new way -- by seed

I've just been examining a tiny, nondescript seed, barely visible on the end of my index finger, and I am filled with a mild kind of awe.

Despite its apparent insignificance it represents a horticultural breakthrough -- table potatoes from seed. That single seed, in fact, conjures up visions of freshly boiled new potatoes, served with melted butter, sprinkled with chopped parsley, and lightly seasoned with a little salt and pepper -- a dish worthy of an emperor's table, in other words.

Until very recently such a vision would have been dismissed as fanciful.

Potatoes, as everyone knew, could for all practical purposes be grown only from tubers. Then, several years ago, the chance discovery in the Andes of a wild potato that produced true seed changed all that. (Strangely, the scientists were out looking for new strains of petunias at the time.)

That potato was brought back to the United States and bred and cross-bred to improve tuber size while still retaining the ability to produce true seed. Further improvements lie ahead, and some forecasts suggest that the bulk of the world's potatoes will be grown from seed within 10 to 15 years.

We shall have to wait and see if that is true, of course.

Meanwhile, the seed is being sold to home gardeners and the bedding plant industry for the first time this year. That means you have two options:

* Grow the potatoes from seed yourself as you now do tomatoes and peppers.

* Or buy started plants from your favorite nursery.

A word of caution, however: If potatoes are a major crop in your annual food-garden program, don't go hog-wild over Explorer, as the new seed variety is named. They are not the perfect potato -- at least not yet. What Explorer won't give you is the large Idaho baking types; what it will give you is a host of small- to medium-sized potatoes, perfect for serving up as fresh-boiled.

If you want large bakers of a size that draws admiring comments from dinner guests, you will need to grow the old-fashioned standbys as well.

Sow the seeds indoors in flats 6 to 8 weeks before you plan to set them out in the garden. Seeds take between 10 and 15 days to germinate. See to it that the seedlings are placed in a well-lighted window or else under artificial lights. There is good reason for this. Eratic or poor lighting during the seedling stage can sometimes trigger early tuber formation. Under such circumstances you'd need tweezers to gather in the harvest.

Potatoes grow best in coolish weather -- which is why the Scots and the Irish are so good at them. So get your seedlings into the ground ahead of your tomatoes (which grow well only in really warm soil). On the other hand, be prepared to throw some sort of covering over the seedlings, should a late frost threaten.

Like conventional potatoes, the Explorer variety does best if it is hilled up with soil or shredded mulching materials as it grows. Or you might set out the seedlings in a trench about 10 inches deep and fill it in as the potatoes grow.

Another option: Dig a series of shallow holes, about 2 feet in diameter, and place three seedlings in each hole. Fill in regularly as the plants grow. According to all reports you should harvest between ''two and three pounds of small to medium potatoes from each of these hills.''

Seeds of the new potato are available from most seed houses. Check with a local nursery. It may well have flats of started plants available this year, too.