At the end of the 1978 racing season, King Leatherbury, Buddy Delp and Dick Dutrow all will rank among the nation's top five race-winning trainers.

The fact that three Maryland-based horsemen should achieve such success is no coincidence, no accident of geography. They have been able to compile their remarkable statistics precisely because they do operate in Maryland-where they enjoy an advantage they would not have elsewhere.

The secret of their success is not principally their skill as trainers. It is not some exotic drug. It is not their unwritten agreement to refrain from claiming each other's horses. Leatherbury, Delp and Dutrow owe their success to something much more basic.

Stalls.

Although they would not be confused with suites at the Madison, throughbred's stalls are valuable. (A track can spend more than $4,000 to build a stall and as much as $5 a day to maintain it). They are crucial to a trainer because the number of stalls he is allotted will define or limit the size of his operation. A man with 10 stalls cannot become a big-time trainer, no matter how many rich owners he has behind him.

Because the supply of stalls is limited, most tracks restrict the number that any trainer may have. The maximum is commonly around 40. In New York, with 2,800 stalls available at Belmont and Aqueduct the limit is 44.

But for the current Laurel meeting, Leatherbury, Delp and Dutrow have 75 stalls each-45 at Laurel and 30 at Bowie. They control one-tenth of all the stalls in the state. Only a handful of other trainers have as many as 25.

No other state has a comparable impbalance of power, and no state has such uncompetitive, tiresome racing as Maryland. The headline "Dutrow Entry Heads Bowie Sprint" seems to appear in the Daily Racing Form about a hundred times a year.

How did Maryland racing get this way?

In a sense, the Big Three was created by Larry Abbundi, racing secretary at Bowie and Pimlico. Abbundi's job is to fill nine fields a day, and he allots stalls to the people who best help him do it.

Leatherbury, Delp and Dutrow not only have good horses; they run them frequently. They helped Abbundi put on a good show, just as they helped Lou Raffetto Jr., racing secretary at Laurel, this fall.

Dutrow, with his 75 stalls, has sent 191 horses to the post at the current meeting. By contrast, Craig Nicholson has 15 stalls and has started three horses. Robert Beall has 18 stalls and has run eight horses. It is sensible and proper for a racing secretary to take stalls away from the Nicholsons and Bealls and give them to the Dutrows.

But this process went too far, until it became counterproductive, hurting the quality of Maryland racing instead of helping it. The bigness of the Big Three's operations gives them so many advantages that the rest of the trainers in the state cannot hope to compete with them.

Abbundi maintained that because Maryland has so many stalls at its three tracks, the growth of the Big Three has not squeezed out smaller stables. That may be true, but the strength of Leatherbury, Delp and Dutrow undoubtedly has kept other trainers from coming to Maaryland.

"I hear out-of-state trainers complain all the time that Maryland would be a good place to race if you didn't have the clique to fight," said Fendall Clagett, head of the state's Horsemen's Benevolent and Protective Association. "People with good stables of 20 and 30 horses simply don't want to come here."

Clagett advocated a limitation on the number of stalls any Maryland trainer may have: 50, or perhaps even 40. The Big Three's friends argue that this would be unfair, un-American, a penalty for success. But oligopolies that inhabit or destroy honest competition are not fair, either.

Matt's War circled the field to register a two-length victory yesterday in Laurel's feature race.

The 3-year-old son of Leematt was ridden by Gregg McCarron and ran the mile in 1:39 2/5, paying $7.60. Jarrett held well to second, nearly two lengths before Lion Lamb.