Even at the Christmas season, it is sometimes necessary to be hard-hearted. So the Maryland Racing Commission last week turned down the bid of convicted race-fixer Jesse Davidson to be licensed as a jockey in the state. It also is taking a long, skeptical look at the application of tipster Mike Warren Lasky to be relicensed as an owner in 1983.

For the people who regulate thoroughbred racing, there is no function so important and so delicate as licensing. The sport has been plagued by many scandals in recent years, and the best way to prevent them is to keep people with questionable records or reputations out of the sport. But defining what type of people should be kept out is not always easy, as the commission's recent deliberations have made clear.

Davidson, a former national riding champion, spent four months in prison for conspiring to fix a race at Bowie on St. Valentine's Day, 1975. Since then he has argued that the circumstances of that "fix" were relatively innocuous and that he deserves another chance. "I've paid my dues," he said.

Davidson may deserve sympathy, because riding horses has been his whole life. But he does not deserve reinstatement any more than convicted embezzlers deserve jobs as bank tellers.

"It has always been our position," said Clifford Wickman, president of the Thoroughbred Racing Protective Bureau, "that people convicted of a felony concerning racing should be barred from the sport." Many racing officials were properly appalled when the Maryland Racing Commission gave trainer's licenses to two of the other jockeys involved in the St. Valentine's Day fix. But if race-fixing jockeys are not forbidden to ride again, is there anything the sport won't tolerate?

The Davidson case was black and white compared to most decisions about licensing, where applicants have records and reputations that fall into a gray area. Too often the decisions of stewards and commissioners in such cases tend to favor the rich and the powerful. Racing officials in several states wanted to put small-time trainer Ray Stifano out of the training business this year, and tried to do it on the basis of a 14-year-old conviction for receiving stolen property. But if the convicted felon of that era happens to be a millionaire horse owner like financier Louis Wolfson, he will be hailed as a patron of the turf.

In the gray areas, commissions must attempt to judge fairly what is in the best interest of racing, and that is what the members of the Maryland board are trying to do after hearing testimony in the case of Lasky. His lawyer argued that Lasky, who runs a mail-order operation to sell tips on horses, was unfairly singled out for special attention. After all, if a race-fixer can get a license in Maryland, how can the state deny one to a man who has never even been prosecuted for a crime?

Maryland's statutes do say that the state may deny licenses to "touts or persons of similar pursuits," or for "conduct detrimental to racing."

There are many who believe that a mail-order tipster who sells supposed inside information on horse races, often hinting that there may be a betting coup in the works, is engaged in detrimental conduct. And people who paid $100 for one of Lasky's tips last fall might describe what he did to them in harsher terms.

Under his professional name Mike Warren, he wrote a letter to prospective clients which said:

"My backstretch sources have ferreted out a super runner . . . so strong that I GUARANTEE THIS HORSE WILL WIN.

"Usually I ask that you pay me after you win, but this is an unusual case -- information so strong that I had to lay out the money in advance. . . The $100 is guaranteed. So strong is this selection that THIS HORSE MUST WIN OR YOU GET YOUR MONEY BACK PERIOD!"

The horse he released, Hail Emperor, did not win. He finished second. So did Lasky's clients promptly get their money back? Not quite. Instead they got a letter.

"Dear Subscriber:

"Our hidden longshot guaranteed winner did just that and won money for all subscribers who played him with confidence across the board and top and bottom in the exactas as we predicted." He proceeded to point out that bettors would have made money if they had bet $200 to win, $400 to place and $600 to show. "You're richer today," he told his clients.

If some of those clients could have gotten their hands on him after that, the Maryland Racing Commission probably would not have to be deciding whether to renew his license as a horse owner.