Texas millionaire Charles J. Ziff looks a little stiff.

A photo session with Ziff, who does not ride, holding the reins of a stunning-looking but skittish thoroughbred has been a mixed success, with the horse nervously pawing at the stone dust and river bottom sand of the vast riding ring Ziff owns here.

Now the 41-year-old Ziff, with beads of horse drool spotting the front of his navy blue polyester blazer, stands, arms crossed, trying to effect the pose of the supremely confident corporate easy rider.

Suddenly, off-camera, actress Linda Blair (the possessed child in "The Exorcist"), an ardent horse fancier and a friend of Ziff's, leaps over to pump a little life into the shot.

"RE-LAX, CHARLIE!" Blair bellows in a hoarse, stagey scream. "LOOK LIKE YOU'RE HAVING FUN!"

Under the circumstances, having fun looks doubtful for this nouveau squire of Virginia horsedom. What he is having, however, is an impact on the state's horse industry and the nation's once-exclusive community of competitive hunter-jumper enthusiasts.

With sizable wealth under his belt from Texas real estate dealings, Ziff has arrived in modest, rural Culpeper County 75 miles southwest of Washington, and virtually overnight, as these things go, has loosed a galloping charge at the conventions of Virginia horse society and nationwide horse meets.

In the process, he has become a burr under the saddle of Virginia officials, openly criticizing the state's decision this year to build a publicly owned horse center of its own down the road in Lexington, which is scheduled to open in 1987.

In Gatsbyesque fashion, he has become a figure of local speculation and mystery, spending money as Culpeper has never seen it spent and leaving the local people to wonder who and what he is.

"He's related to Ziff-Davis," a publishing empire, confided one Culpeper businessman in an interview last week.

"Not true," said Ziff. "I wish I were."

There is his land, 200 acres purchased three years ago for $1 million and developed, at a cost of $5 million, he says, into Commonwealth Park, a premier horse show facility that this year has drawn the country's best riders and best horses to compete for rich purses endowed by Ziff.

"One of the four major facilities in the world," as Ziff tirelessly touts it, his finger gleaming with a gold, horseshoe-shaped ring as he hands out a videocassette lauding the place's virtues.

To help spread the hunter and jumper gospel, Ziff cut a deal with the Virginia Beach-based Christian Broadcasting Network to televise many of the events on cable. To help fill the stands with spectators, twice this year he had an airplane drop as much as $2,000 in cash on the crowd.

"That drew some local interest," said a grinning Culpeper resident.

The motif of the sprawling grounds is haut theme park, with show rings, stalls, a restaurant, a clubhouse, tennis courts, a swimming pool, retail shops and a press box all spanking new. "It's made its way much quicker than any place I've known," observed preeminent British course designer Pamela Carruthers, who is on the Ziff payroll. "Most places take much longer."

Only a new word could capture it: horsesport. The sign at the entrance reads: "Commonwealth Park: Horsesport in the Virginia Tradition."

Convinced that "horsesport" needed an injection of entrepreneurial gusto, Ziff even created his own competitive niche, the U.S. Grand Prix League, with the "U" and the "S" overlaid in gold to form the unmistakable image of a dollar sign.

If some traditionalists find that approach too crass, Ziff appears not to care. "In the past, it was a private club," he said. "They looked at it not as a sport but a social event . . . . This is 1985. Hunters go for $200,000 to $250,000. Jumpers cost from $100,000 to $1 million. It's a business."

To put some pizazz into his operations, Ziff recently hired actress Blair as a spokeswoman for Commonwealth Park and the U.S. Grand Prix. She is a believer. "I've dedicated my life to the sport ," she said grandly. "This is the horse rider's dream."

Propelled by his energy and his money, Ziff appears to be having his way in putting his place on the map in a hurry. Actors Robert Duvall and Sissy Spacek, who both own farms in Virginia's horse country, have been recent guests at the park. Perhaps more significantly, Ziff has won over some key keepers of the horsesport flame.

"He's been a substantial influence on the sport," said writer Peter Winans of the Middleburg-based Chronicle of the Horse magazine, who refers to Ziff as "this hurricane who blew in from Texas." Competition inspired by Ziff, particularly with an older rival, the American Grand Prix Association, "has been healthy, in my book," Winans said.

Although the early line on Ziff's efforts was that they were "foolhardy," according to Winans, "he's gone about it 100 percent right . . . . I personally like the guy."

The writer credits Ziff with helping open the pastime to the young with scholarships and notes approvingly that Ziff recently was host to members of the U.S. Pony Club from across the country at his expense.

It was his own son, in fact, who helped draw Ziff into the Culpeper connection.

A Westport, Conn., native who attended the University of Alabama and earned a law degree at Memphis State University, Ziff said he moved into real estate in Dallas about eight years ago. He found himself working 18- to 20-hour days. "I had a bleeding ulcer. I had a blood count of four. I was dead."

Advised by his doctors to ease up, he started accompanying one of his three sons, David, to equestrian events around the Southwest, some of them at publicly owned fairgrounds. He says he was unimpressed. "A lot of horse shows in that part of the country, to put it bluntly, were the pits."

When the Culpeper property, then known as Showday Farm, went up for sale in 1982, Ziff grabbed it. Commonwealth Park followed.

Coincidentally, Virginia officials, after considering it since the late 1970s, committed themselves to an ambitious horse center in Lexington that had been avidly sought by members of the state's horse breeding industry. Although the center will be the product of a state and industry partnership, the very idea of government involvement stirs Ziff's competitive juices.

"It makes no economic sense to have a second facility to compete with one of the four best private facilities in the world," Ziff huffed. "They want to use state money to build it and state money to subsidize it. It's for a small segment of the public. I don't think that's right."

The Virginia Horse Center's revenue projections are misleading, he charged, and its $4.2 million cost estimate is unrealistic. "Seven million," he said. "It can't be built for under $7 million, I'll tell you right now."

Not so, say state and private proponents of the project, who note that the plans, approved overwhelmingly by the General Assembly and signed into law last spring by Gov. Charles S. Robb, call for a much less commercial, less intensely promoted operation than Ziff's.

Backers of the center also point out, with quiet amusement, that Ziff offered to sell his beloved Commonwealth Park to the state for $5.5 million when a site selection committee was touring the state a year ago. The offer was rejected.

"The push for the project came from the private sector, the horse industry, not the government," said James Sharp of the Virginia Department of Agriculture and Consumer Services. "It's not something being forced on the taxpayers or Mr. Ziff."

Ziff the businessman conceded that while his spread is "not listed and not on the market," he would listen if somebody made him an offer he could not refuse.

After all, being the king of Commonwealth Park isn't all cantering and standing around in the winner's circle. Ziff may break into the black by 1986. "It's a very expensive proposition," he said, adding that he spent $400,000 building the show rings alone. "You have to have a deep pocket to start out with, which I continue to have."

Still, just to show that competition can be fun, there is the true story about a corn-on-the-cob eating contest between Ziff and John (Monk) Reynolds, the former owner of Showday Farm. "He ate 29," Ziff said. "I ate 28."

On the other hand, he added, "My wife didn't talk to me for a month. She said it wasn't in good taste."