Holly Hepp of Middleburg circled her horse, Damien, around their dressage trainer, guiding him through a series of precise movements as all three prepared for what could be the most important competition of Hepp's life.

"He will trust you more and more," trainer Sandy Phillips said of Damien, a 12-year-old Thoroughbred-cross. "Keep his neck floating down. Watch his neck."

As Damien lowered his head and rounded his neck, his weight shifted from shoulders and front legs to the more powerful muscles of his hindquarters, which he could use more freely to propel and balance himself.

"There, yes," Phillips said. "See what I mean?"

By the time she and Damien left the ring, Hepp's face was ruddy from the workout, the sweat brought out by the early morning sun. They would return the next day for show-jumping practice.

The 31-year-old Hepp has good reason to work hard: She is one of 13 riders short-listed for a spot on the U.S. three-day eventing team at the Olympic Games in Athens, a competition that combines dressage, a cross-country course and show jumping. Some call it the "equestrian triathlon."

All 13 riders were at Stonehall Farm in The Plains last week for their final training session before heading to the Horse Park of New Jersey in Allentown on Tuesday. A competition there will determine their fate by narrowing their ranks to the five riders and five alternates who will go to Greece. Three riders will have to wait four more years for another chance.

Among the riders on the short list this year are, as usual, a handful of local residents, with six competitors from Loudoun and Fauquier counties. But the list bears many names that have not appeared in the past. Only two have competed in the Olympics.

The faces of top three-day eventers are changing, competitors say, as a new generation of riders comes up through the ranks. Such riders are by no means baby-faced newcomers to the sport -- competitors tend to count advanced age as an advantage -- but they are emerging from the shadows of such long-time greats as five-time Olympian Bruce Davidson, who is now in his fifties.

Veteran riders "are still active, but to some extent, they're stepping aside a bit and making room for another generation," said Bluemont resident John Williams, 39, who made the short list for the first time this year with his horse, Carrick.

Hepp, also on the short list for her first time, is part of that new generation. For her, just making the short list was a momentous occasion. ("Oh, my gosh. It was an absolute dream come true.")

But no matter which riders are selected for the team, Hepp said, they will have a "really good shot this year because there are a lot of hungry people out there."

It could take more than hunger to bring back the gold in the three-day event, a competition that riders describe as testing a horse in almost every way possible. In dressage, on day one, a horse completes difficult gaits and movements at the subtle urging of its rider. The next day, rider and horse must navigate a 3.5-mile cross-country course with fences, ditches and other obstacles that test endurance and agility. And on the final day, when both rider and horse are nearly tuckered out, comes the show jumping.

Part of the challenge, riders say, is that a horse needs to be able to adapt quickly and easily to the task at hand. Often, the type of horse that "can accelerate on a dime" and "has a capacity for distance" on the cross-country course is not the type to appear relaxed and obedient during dressage, said Jan Thompson, 36, of Purcellville.

"Sometimes it's not so easy," said Thompson, who will be in New Jersey next week to compete for a spot on the team.

David O'Connor of The Plains knows the challenges as well as anyone. O'Connor, the gold medalist at the 2000 Games in Sydney, is seeking another shot at gold in Athens. At 42, he is regarded by riders as the backbone of the American contingent and the bridge between the competitors of years past and those of the future. His wife, Karen O'Connor, a two-time Olympic medalist, is an alternate on this year's short list.

It is rare to have so many people without Olympic experience on the list, David O'Connor said. But he added that their lack of experience at the Olympics gives them a certain energy that bodes well for the future.

"You need that drive and that passion to make things happen," he said.

The team that lacks Olympic experience follows guidance from a head trainer who has plenty. Mark Phillips, the riders' chef d'equipe, won the gold medal in the three-day event at the 1972 Games in Munich and the silver at the 1988 Games in Seoul. He is also husband of Sandy Phillips, the dressage coach, and former husband of Britain's Princess Anne.

Williams, who rides Carrick, is no novice himself, having competed for 25 years and placed fourth at the World Equestrian Games in Jerez, Spain, two years ago. Had it not been for an unfortunate fall during a major selection trial for the team in 1992, he said, he probably would have made it to the Barcelona Games. Now he's seeking a shot on the Olympic team -- once again, for the first time.

Holly Hepp, 31, riding Damien, a 12-year-old Thoroughbred-cross, works out in the ring at Stonehall Farm in The Plains. Hepp, of Middleburg, is one of 13 riders short-listed for a spot on the U.S. three-day eventing team at the Olympic Games. Five riders and five alternates will go to Greece.Stephen Bradley practices as head trainer Mark Phillips watches. Phillips, left, won the gold medal in the three-day event at the 1972 Games in Munich and the silver at the 1988 Games in Seoul.