"DON'T WORRY," instructor Amy says after my fourth attempt to swing a leg over my horse. "When I started riding again after 10 years I couldn't mount the horse either."

Although she seems at the moment an insurmountable object, Brandy is in fact one of the gentlest of the 60-odd horses at Rock Creek Park Horse Center. She was chosen for me after I phoned for a lesson appointment and was asked my height, weight and riding history by the safety-minded horse center. I am relieved to learn of her reputation for mildness. I have the classic non-athlete's fear of fast-moving balls and horses. Last year I took up tennis, and now I deal with balls every day. I figured it was time to conquer my fear of horses as well.

"You don't want to lose that completely -- fear of horses is quite common and very healthy," says Amy. "Well, actually I wouldn't say fear but respect . . ."

It wasn't easy to choose among the large number of horse stables around Washington. An aspiring equestrian can take English- or western-saddle, balance or hunt seat, boisterous trail riding or structured lessons. Rock Creek offers a good mix. It has a solid lessons program, plus more than 40 miles of trails through some surprisingly sylvan sections of Rock Creek Park.

Besides its central location at Military and Glover roads NW (near the Maryland line, about a mile from the Friendship Heights Metro stop), the horse center offers lessons as late at 8 p.m., making it a convenient after-work stop. Many area stables offer such accommodatingly late lessons.

Here I'll learn English balance seat. This means using an English saddle (the one with no horn to grab) and riding in sync with the movement of the horse rather than working against it. The other common seat taught in the area is "hunt," in which the rider sits up and forward in the saddle. "For beginners this is a rather precarious position but it does increase speed," Amy says when I ask about the difference. I have a while to go before I'm joining any fox hunts, so I won't worry.

I like Amy's teaching style. As we groomed and prepped the horse for the ride she talked about the animal. She gave me basic, general tips such as "never walk around the back of the horse, you might get kicked," and some that were specific to Brandy. (Horses have foibles, too: She was girthed too tightly once as a foal and reacts badly to sharp pulls on the girth.)

I think Amy has compassion for the adult beginner because she came late to the profession herself. Although she grew up on an Indiana farm and rode in Girl Scout camp, she dropped horses after she got to college and discovered boys. After working as a social worker for a few years, she decided to go into teaching therapeutic riding. She took lessons at Rock Creek, and was eventually hired as an instructor.

My lesson is being held in one of Rock Creek's most useful facilities, an indoor riding ring. At the moment, it's pouring rain outside. We spend most of the lesson on fundamentals; this turns out to involve unlearning most of what I was taught as a kid and on various laissez-faire trail rides. At Rock Creek, as at any serious horse center, you learn to work with the horse, not against it.

"You'll never win a battle of strength with a horse," Amy says. So "kick the horse" becomes "squeeze the horse gently with your calves" to get her going. "Pull back on the reins" becomes "gently resist, than ease up, then resist again, she'll stop." Believe it or not, this works. I am thrilled. I'm actually guiding the horse, and she's responding. By the end of my hour lesson I am trotting 'round the ring and feeling like a pro.

Okay, so in my sweats and high-heeled boots and pink cashmere jacket (a silly choice, since horses might be charming but they're also usually dirty), I'm not going to remind anyone of Elizabeth Taylor in "National Velvet." Nor of the confident Kate Hepburn, crop in hand for a morning jaunt on horseback. When I was young, those were the visions that drew me to riding. And after a summer at a riding camp for kids, I boasted a terrific china horse collection, swollen ankles and fear of horses. These days my aspirations are more attainable.

I'd like to be able to feel confident riding for pleasure, probably trail rides first, then to be able to rent a horse -- for both the physical and psychic benefits that come from this kind of ancient outdoor exerise. And can the hunt be far away?

Here's a sampling of area stables.

DISTRICT ROCK CREEK PARK HORSE CENTER -- Military and Glover roads NW. 362-0117. Horse rental $11 an hour. Guide provided; 40-plus miles of trails available. Private lessons $23 a half-hour, group lessons $16 an hour. English balance seat taught. Therapeutic riding program. Hard hat required for lessons. Boarding available at $300 to $325.

MARYLAND CAMP OLYMPIC -- 5511 Muncaster Mill Rd., Rockville. 926-9281. No horse rental. Private lessons $30 an hour, semi-private $20, group $15. Hard hat required. Summer camp for kids from three to 14, $90 a week. Boarding available at $175 a month. CIRCLE N RANCH --

1234 Briggs-Chaney Rd., Colesville. 384-1995. Rental not available. Private lessons $14 a half-hour, semi-private $27 a half-hour for 3-person group (divided among them) or $20 a half-hour for 2-person group, group lessons 10 one-hour lessons for $110 or 20 one-hour lessons for $200. Hard hat required. No boarding. COLUMBIA HORSE CENTER -- Columbia. 301/776-5850. Rental not available. Private lessons, $20 a half-hour; semi-private lessons $20 a half-hour (split between two students), group $15 hour English saddle hunters and jumpers taught. Summer camp for kids, $150 a week (first week), $125 each succeeding week. Hard hat required. Boarding $10 a day for Columbia residents, $11 a day for non-Columbia residents. Therapeutic riding program. Horses bought and sold. DOUBLE S STABLES -- Branch Avenue, Brandywine, 12 miles from Beltway Exit 7A. 372-8914. No lessons. Horse rental $12 an hour, no guides; 100 acres of fields and trails. Offer both English and Western style riding. Boarding is $130 a month. Horses bought and sold. J AND J STABLE -- 211 Ednor Rd., Silver Spring. 774-4899. Rental not available. Lessons for both adults and children, private lessons $22 an hour, group $115 for a series of 10. English saddle taught, hard hat required. Boarding $170 a month. Ponies for parties. MARYLAND HORSE CENTER -- Quince Orchard Road, Gaithersburg. 948-8585. Cross-country guided trail rides, $16 for 1 1/2 hours geared to beginning riders. Private lessons $35 an hour, $40 for jumping; semi-private (3 students at the most) $25 an hour. Group lessons from $15 to $20 an hour depending on level of rider. Summer camp for children. Rates vary on level of rider. Adult camp, $125 a week. English saddle taught. Hard hat required. Boarding $325 for straw bedding, $380 for shavings. MEADOWBROOK STABLE -- Meadowbrook Lane, Chevy Chase. 588-6935. Private lessons, $26.50 a half-hour, $48 an hour; group lessons, on a semester basis, $335 for 18 classes, $175 for evening series of 9 classes for adults only. They offer a summer day camp for children at $220 a week. Boarding $330 a month for horses, $320 a month for ponies. Horses bought and sold. MERRYMOUNT HORSE CENTER -- Frank Tippet Road, Upper Marlboro. 868-2109. Rentals not available. Private lessons $15 a half-hour in a series of 4, group $57 a month (once a week). English saddle. Hard hat required. Summer riding camp for kids, $120 a week. Board $215 a month. ROCK BOTTOM FARM RIDING SCHOOL -- 21930 New Hampshire Ave., Brookville. 924-2612. Trail rides, unguided at $18 an hour, guided at $20 an hour. Private lessons $30 an hour, semi-private $20 an hour, group lessons $18 an hour. Summer discounts available on children's lessons. Hard hat required. Boarding available from $217 to $337 including 4 lessons. WHEATON PARK STABLES -- 1101 Glenallan Ave., Wheaton. Phone 622-3311. Rental $8.50 an hour on weekdays, $10 on Sundays (available to those currently taking lessons at Wheaton), guided trail rides on Sundays only for $10. Group lessons $150 for 12 one-hour lessons. Summer camp for kids, two-week session $175.

VIRGINIA BRIARY FARM RIDING ACADEMY -- 2405 Parkers Lane, Alexandria. 765-8007. Rental not available. Private lessons only, $30 an hour or $15 a half hour. Hard hat required. Boarding available at $130 to $250 a month. GREAT FALLS HORSE CENTER -- Arnon Chapel Road, Great Falls. 759-3400. Private lessons, $40 an hour, group $17 an hour. English balance seat taught. For more experienced riders they offer a combined training program. Hard hat required. Summer camp for kids $200 a week. Therapeutic riding program. Boarding about $285. JUNIOR EQUITATION SCHOOL -- 9710 Clark Crossing Rd., Vienna. 938-2383. Rentals not available. Private lessons $35 an hour, group lessons $180 for 10 weeks of 1 1/2 hours of lessons (one hour mounted, one-half hour theory). English saddle taught. Hard hat and full riding attire required. TAMARACK STABLES -- 8901 Old Colchester Rd., Lorton. 339-5160. Rentals not available. Private lessons $24 an hour, semi-private $18 each per hour, group lessons $10 per hour. English and western saddle taught. Hard hat required. WOODLAWN STABLES -- 8907 Richmond Highway, Alexandria. 780-7220. Rentals not available. Private lessons $30 an hour, $145 for a series of 5, group lessons $130 for a series of 10. English balance seat. Hard hat required. Boarding approximately $270. Horses bought and sold.