YOU CAN LEARN to fly a hang glider over a single long weekend, the experts say, if the weather's good and everything goes just right. Which it usually isn't and hardly ever does. And anyway that's just the beginning.

"Weather and wind direction absolutely control whether we can fly," said Jerry Nielsen, president of the Capitol Hang Glider Association. "We've had a run of really rotten flying weather for the past couple of years, and that's turned off a lot of beginners who just haven't been able to get in flying time. And it seems like every time we find a good training hill, somebody comes along and builds apartments on it."

The Washington club has launched a training site development drive. Meanwhile, weekend (and some weekday) lessons are available from the following local instructors, all certified by the U.S. Hang Glider Association:

Eric Logan (vice president of Capitol Hang Gliders) and Bill Criste (director of USHGA Region 9), trading as the Pennsylvania School of Hang Gliding. Beginner to advanced training. 717/762-7858.

Richard Hayes (described by Nielsen as "one of the top pilots and teachers, at all levels"). 301/628-1684.

Santos H. Mendoza of Vienna (who says he's had nearly eight years of teaching everyone from teenagers to septuagenarians). Certified for beginner-level instruction. 573-3861.

Fees range from as little as $10 for an introductory lecture session to $75 for individual flying sessions. Preflight practice on a simulator has become standard, which saves a lot of twisted ankles and scraped knees.

While a good student with a good teacher on a good training slope in good weather might get his novice "Hang One" rating in three days of practice, it takes six months to a year of practice to advance to the point of being able to step off a cliff and soar safely among the mountains.

If you have doubts about the credentials of an instructor, check him or her out with the U.S. Hang Glider Association (213/390-3065). No matter what your instructor's rating, if you have trouble understanding what you're being taught, or lack confidence in the person, find somebody else.

The best place in the East to learn hang gliding, everybody seems to agree, is at Kitty Hawk Kites in Nags Head, N.C. The school offers instruction daily the year around, weather permitting, and at Nags Head the weather permits hang gliding three days out of four. All flights are made from soft, forgiving sand dunes, and you can wash off the sweat and sand in the ocean afterward.

It is wonderfully appropriate to learn to fly within sight of where the Wright brothers did, but Kitty Hawk is now doubly appropriate, because it's the retirement home of Francis M. Rogallo, the NASA researcher who invented the hang glider (he tested his designs by hanging his children out to fly).

Schedule a week at the beach, which is well worth the trip by itself, and you can take the three-lesson ($89) or the six-lesson ($170) beginner package. Perhaps one student in five gets to Hang One within three lessons, a spokesman said, and a hefty majority do so within six lessons, "although it all depends on the wind; bad wind makes slow learning." 919/441-6094.