You don't have to like horses to like Loudoun County, Va., but it helps.

Without horses, much of Loudoun County wouldn't exist as we know it today. The love of horses appears to permeate everything, and much of the open land of the county is devoted to them.

This beautiful rolling countryside of the Piedmont Plateau, bounded by the Potomac River on the north and east, Blue Ridge Mountains on the west and U.S. 50 on the south, is the northern end of Virginia hunt country. The country also boasts two stately homes that are open to the public, and even they continue horse associations stretching back nearly 200 years.

We plunged into the horse country, visiting the two homes, taking a horseback riding lesson and attending the Virginia racing season's last point-to-point event, sponsored by the Loudoun Hunt Club.

Our weekend began on Saturday at Morven Park, on the western edge of Leesburg, about 30 miles northwest of Washington. The home's present association with horses is the International Equestrian Institute, which is housed on part of the estate's 1,200 acres. From the past, there is the Morven Park Carriage Museum with 125 horse-drawn vehicles representing 100 years of early transportation.

The estate boasts the distinction of being the home of the governors of two states: Thomas Swann of Maryland in the last century and Westmoreland Davis of Virginia in this century.

The white mansion , framed by acres of lush, green lawn, was begun in 1781 by Maj. Thomas Swann, father of the Maryland governor. The original fieldstone farmhouse grew into a 31-room mansion, 18 of the rooms open to the public and operated by the Westmoreland Davis Memorial Foundation. Tours, with a guide, cost $1.75 per adult, 75 cents per child and include the carriage museum, nature trails and picnic grounds.

Few traces remain of the Swann family. Davis, who served as Virginia governor from 1918 to 1922, bought the estate in 1903 and he and his wife, Marguerite, filled it with European antiques, some of them comtemporary reproductions. Morven Park now has one of the finest collections of European period furniture to be seen in the United States.

Marguerite Davis appears to have been a bit eccentric. She had a habit of leaving curious signs about the place. One still in the kitchen warns employees that anyone "mixing garbage in cans will be fined $1."

The governor was master of the hounds in the Loudoun Hunt Club at one point and a game room and huge potrait of him in his jodhpurs attest to his hobby. Behind the house is the stable area, which houses part of the collection of horse-drawn vehicles and - strangely out of place - a 1956 Continental, the last car owned by Mrs. Davis. Except for the car, however, there is not identification on any of the carriages.

But down the path in a corrugated metal building are more than 100 additional carriages, coaches, surreys, wagons, sleighs, plus a fire engine and a hearse, all described in detail. The carriages actually were collected in Warrenton, Va., by Viola Townsend Winmill, who died last year. Her collection, later augmented, was moved to Morven Park in 1969.

Morven Park can be reached by taking Rte. 7 west from Leesburg. Just at the edge of town is a sign leading north along Morven Park Road. Turn left at the end, onto Old Waterford Road. After about 100 yards, there is a sign for the park.

Oatlands, about six miles south of Leesburg on U.S. 15, is part of a 256-acre estate operated by the National Trust. The 13-room mansion, although uniquely designed, doesn't compare with Morven Park in antiques, but it does feature an octagonal drawing room and two semi-octagonal staircases on each end of the house.

Oatlands was begun around 1800 by George Carter and, like Morven Park, additions were made over the years. Oatland is a very light, attractive, airy home and outside are elaborate boxwood gardens. The charge at Oatlands is $1.50 per adult, 75 cents per child.

Mr. and Mrs. Wiliam Corcoran Eustis bought the estate in 1903. Like the Davises at Morven Park, the Eustises put their own stamp on Oatlands. He was the grandson of the founder of the Corcoran Art Gallery in Washington and she was the daughter of President Benjamin Harrison's vice president, Levi P. Morton. She died in 1964, and her daughters gave the estate to the Trust.

For dinner that evening we chose Leesburg's Green Tree Restaurant, a spacious colonial-style restaurant that prides itself on a limited menu of authentic dishes culled from recipes of the 18th-century - including some of Thomas Jefferson's - prepared in the original manner.

The menu is fun to read, with desciptions of some of the meals and quaint directions for fixing them. We had curried chicken and something called "Robert's Delight." The chicken recipe originally included instructions for four courses to be served by "Indian boys," but the menu admits the restaurant diverges from instructions on that points. The menu does explain, though, that the curry for the chicken is prepared from scratch.

Robert's Delight is a concoction of rolled beef and herbs. Both dishes were good, although the beef tended toward blandness. The entrees range from $6 to $10, with side dished included. A strange collection of early American drinks bearing odd names, most of them mixtures of fruit juice and rum or liqueurs, also are offered. With one of those each, black walnut rum pie and coffee, the dinner for two came to $30.

On Sunday morning we drove to Prucellville to join a group of friends meeting us at the 250-acre North Fork School of Equitation run by Kay Russell. Three of us had been coerced by our companions into taking lessons at $7 each, but we ended up enjoying them very much.

The lesson includes instruction on brushing down the horse and putting on the bit and saddle. The instruction is precise, right down to how to hold your foot in the stirrup. The saddles are the small English type used in fox hunts and not the western style for cowboys. The lesson ended about 1 1/2 hours later after we had learned to ride at a trot while "posting," or bouncing just one of the saddle in rhythm with the horse's movement.

Russell doesn't encourage single lessons, and they usually are given in groups of 10, but she has one of the few farms in the area that will give lessons without the student signing up for a year-long package. Most of her business is a weekend riding camp, including accommodations.

Horses can be ridden without lessons at the Orchard Hill Riding Stables just off Rte. 611 between Middleburg and Purcellville. Run by Marilyn Grubbs, the stables offer western or English saddles and a suitable horse at$5 an hour for unconducted rides on trails around the 60-acres farm. All-day guided trail rides cost $20.

After our riding lessons, the group loaded up a picnic cooler and headed back to Oatlands for the last point-to-point race of the Virginia hunt season, held on the grounds of the estate at a cost of $3 per person. Other equestrian events, including races and shows, are held throughout the spring and summer.

A point-to-point race is a type of steeple-chase, over timber, bushes or other obstacles or flat out over open country. People sit with picnic baskets and binoculars on a hill in the middle of the meandering course or, if they are patrons of the hunt, drive close up with their large station wagons, lower the tail gates and spread fancy meals. Some of these spreads included flower arrangements, fancy table cloths and silverware. Candlelabras have been seen on tail gates at some races.

This weekend cost us about $70, including the picnic but excluding about 180 miles worth of gasoline we used in driving the pleasant Loudoun County roads. The $70 included $14.56 for a double room at the Piedmont Motel between Oatlands and Leesburg. Though nothing special, it was more than adequate for the price.

For information about Morven Park, write to Rte. 2, Box 50, Leesburg, Va., 22075, or telephone (703) 777-2414. For Oatlands, it's Rte. 2, Box 352, Leesburg and (703) 777-3174. Both are open 10 a.m. - 5 p.m. Saturday, 1-5 Sunday. For reservations at the Green Tree (we didn't need them), the address is 15 S. King St., Leesburg and phone (703) 777-7246.

Kay Russell at North Fork can be reached at (703) 338-7474. Marilyn Grubbs at Orchard Hill is (703) 554-8255. Both will provide directions to the farm and they do recommend reserving for weekends. There is no central place that lists upcoming equestrian events, but the weekly newspaper, The Chronicle of the Horse, published at Middleburg, Va., 22117, prints a calendar of events in the first issue of each month.