What is the richest horse race in Maryland?

A. The Preakness.

B. The Laurel Futurity.

C. The Washington, D.C. International.

D. None of the above.

The answer will be "D" after tonight, when the $320,225 Potomac Stakes is contested at Freestate Raceway. If it seems amazing that harness racing, long considered the poor cousin of the thoroughbred industry, should offer the richest race ever run in the state, it is doubly amazing because the event didn't even exist two years ago. The Potomac offers dramatic evidence of the growth of Freestate and the harness sport in general.

Before Frank de Francis bought Freestate a few years ago, the most memorable thing about the track was the fact that you would sometimes be placing a bet as raindrops kept fallin' on your head--through one of the numerous holes in the leaky roof. But tonight's race hardly belongs on the leaky-roof circuit. It has attracted so many good 2-year-old pacers that the Potomac will be run in five divisions (the third, fifth, sixth, eighth and 10th races) and the track's public relations man says, "I guarantee you there's a world champion in there somewhere."

Billy Haughton has brought five colts to Freestate, one for each division. The most notable of them seems to be Signed N Sealed, who paced a 1:57 3/5 mile at the Meadowlands recently. The great Herve Filion will drive and horses from the Stanley Dancer and John Campbell stables are represented.

How did the Potomac get to be such a big race so soon?

"When I took over here," de Francis said, "I was saddled with a stakes program whose richest race was $20,000. I wanted to be as aggressive on the racing end as I was with promotions and giveaways. Good racing develops the interest of bettors and it attracts the attention of the industry itself."

Having made this commitment, de Francis had a perfect model to emulate. The Meadowlands pioneered the modern era of big-money harness racing by asking owners to pay a succession of nominating and sustaining fees before they could get their horses to the starting gate. To compete in the Woodrow Wilson Pace, for example, owners have to pay a total of $16,000, but they are willing to do so because the purse is $2 million.

Freestate has done the same thing on a slightly more modest scale. Owners have to make four payments totalling $1,700 to start a horse in the race; the track contributes a bit more than $100,000 to the total pot. If harness horsemen choose to support such a race, an enterprising promoter can put on a major attraction. De Francis has swiftly gained that support, and with it he can entertain grand dreams for the future.

"Where will this race be two years from now?" he asked. "The sky's the limit. I certainly think that a purse of three-quarters of a million is in range. That may sound mind-boggling, but if I told you two years ago that we'd have a $320,000 race, you would have said, 'Hey, Frank, come on.' "

He's right.