The ride through gracefully rolling Virginia farmland, past meadows divided into pleasing geometrical patterns by the distinctive white fences of horse country, held out the promise of a special excitement. An afternoon of steepleshasing is unlike any other day at the races.

The narrow road leading to picturesque Glenwood Park in Middleburg was overhung by grandfatherly trees, bent with age but still dignified, their huge, gnarled roots exposed beside the sunken pavement.

Cars were backed up along this road for miles on a recent Sunday, and hardly a chauffeur driven Bentley among them. It has not always been that way the day of the Middleburg Hunt Race Association's spring meeting, but steeplechasing is growing in popular appeal.

Not that it is likely to become a mass sport in the United States. It still has stifling overtones of snobbery, but is no longer the exclusive province of those in the Social Register.

"What always caught the eye of photographers were the Roll-Royces and fancy luncheon spreads with champagne and candelabras, and consequently those those were the pictures that got into magazines," says Charles Colgan, executive secretary of the National Steeplechase and Hunt association, which governs the sport in the U.S. and sanctions a circuit of professional races with purses of approximately $1 million.

"The average person concluded that this was only for the landed gentry, but that impression is changing. The sport is catching on. Now you are likely to see family outings and the college-age crowd instead of just fancy dans."

Of the 11,000 spectators at Glenwood Park - or the 20,000 expected for the Viriginia Gold Cup, timber jumping's Kentucky Derby, at Warrenton next Saturday - a relatively small number lunch on cucumber sandwiches and steak tartare.

The idle rich and insufferably prepie are still visible, to be sure. Genteel Middleburg's "Jump Into Spring" weekend featured a parade of antique coaches, driven by gents in various degrees of formal dress for whom kid gloves and bowlers or top hats were as standard as clipped accents.

Men of patrician birth or aspriation wore red carnations in their lapels and ribbons - "Patron" or, better yet, "Benefactor" - pinned close to their old school ties. The nibbled at a sumptuous buffet and struck poses suitable for the window od Brooks Brothers.

More stuffy still were some of the private picnics. One, set at the boot of a gleaming Rolls bedecked with vases of jonquils and tulips, covered four linen-draped tables. Eavesdroppers learned, through the drift of trivial conversation, that the salmon mousse was divine. What, no truffles? Have another Bloody Mary and try the goose.

But this was only one segment of the audience. For $3 general admission, thousands picnicked on blankets or from the tailgates of humble Chevys and Toyotas.

Ice chests filled with beer and coldcuts outnumbered those bearing caviar. Barbecue sandwiches were on sale at concession stands. The great middle class minglesd with the upper crust, and the hoi polloi appeared in the person of a denim-clad motorcyclist, scruffy and loud, whose T-shirt expressed disapproval of helmet laws in coarse terminology.

A couple of bookmakers set up shop on the terraced hill between the weatherbeaten grandstand and the box seats, scribbling on chalkboards.

"Step right up. No waiting here. Name your odds," yelled a bald man in gray three-piece suit and brown shoes badly in need of a shine. He worked out of an airlines bag, beer in one fist and chalk in the other, handing off incoming cash to an assistant who recorded transactions on pale green cards.

When President Kennedy came here, the bookies were chased away by Secret Servicemen. They are occasionally harrassed by the IRS, but generally left alone to service those who think horseracing cannot go on without gambling. But they get little action because their odds are outrageously bad.

Steeplechasing is an exciting, colorful racing spectacle, more varied and demanding than the short sprints on a flat track that account for most thoroughbred racing in America.

Steeplechase horses carry more weight (130 to 175) pounds) over much longer distances. The course, marked with flags, are mapped out of the natural terrain, over rises and valleys, through fields and woodland.

In jumping races, horse and rider must clear anywhere from a dozen to 22 barriers, ranging in height from three to five feet. These fences can be made of solid timber (popular primarily in Maryland and Viriginia, brush, or wood and plastic.

Since most steeplechasing takes place in states without parimutuel wagering, it attracts fans who appreciate horsemanship rather than the large percentage of bettors that frequently make up the crowds at he flat tracks.

Steeplechasing a mateur and professional, centers locally around Middleburg and Maryland's Green Spring Valley.

The pro circuit is a hybrid of "hunt meetings," of which Middleburg is typical and a limited number of jumping races at major tracks. Last year $608,292 in purses was distributed at the hunt meets, $316,875 at the tracks.

"The whole thing is building up. It's not much money compared to flat racing, but in another couple of years riders and trainers might be able to make a living with jumpers," says Paul Fout, a partner in the Middleburg Training Center - an impressive complex of barns, training and schooling fcilites that resembles the backstretch of a track. Twelve trainers currently stable 220 horses here.

Most leading steeplechase trainers train flats as well as jumpers. The principal income comes from flat racing, a billion-dollar industry that operates, usually nine races a day, at tracks all over America. But steeplechasing offers an extra dimension and special satisfaction.

"It takes more time and patience to make a jumper, and it develops good all-around horsemanship. Most of the good horsemen today have been jumping horse people," says Burley Cocks, who trains 20 jumpers and 20 flats at his 110-acre farm in Unionville, Pa. He has been at it since 1940, after an injury ended his career as a rider.

Jumpers are trained as thoroughbreds are in Europe, on the farm, at a more leisurely and healthy pace than is usually possible on crowded and hurried backstretch tracks. They are shipped olut the day before or the day of a race, and shipped back home immediatley afterward.

Rules prohibit jumping horses before August of their third year because younger horses are not strong or developed enough for several-mile runs over hurdles. The peak age is usually between 4 and 8, but some jumpers go much older. England's beloved Red Rum, for instance, last year won the Grand National at Aintree - the world's most gruelling and famous steelpechase - for the third time at age 12.

"The older the better sometimes, because a horse can never learn too much," says Cocks. "It's efficiency in jumping that wins steeplechases. You want a horse that's got speed, of course, but also an experienced jumper who can clear all those fences and never make a mistake."

Most jumpers were tried originally on the flat, where far more substantial purses can recoup on investment quicker. Those that don't work out for any number of reasons but are sound and strong can be schooled to jump.

A few are bred or bought specificially for jumping, but this is fairly rare.

Not so with steeplechase jockeys, most of whom grow up around the sport and graduate from pony clubs. Jumping riders are bigger (usually about 135 to 140 pounds) than flat jocks (seldom above 105 pounds). Because their mounts do not always clear fences, they hit the ground shipped out the day before or the day.

Steve Cauthen, the top flat jockey last year, earned about $600,000.Jerry Fisback, the leading steeplechase reinsman in 1971-73-74-75-77, earned about $25,000 last year.

"Your riding career is limited. By about 35, your reaction time isn't quick enough to keep up with the young fellas and you don't recover from falls as well, so you start thinking about a new job. Most of us look forward to training horses," says Tom Skiffington, 27, who has challenged Fisback for supremacy in a stirring rivalry since 1975, when he returned from a 2 1/2-year stint riding in England. He finished second in '75, first in '76, and second in the tightest duel of all last year.