After years of controversy, Maryland's thoroughbred racing commission today adopted stringent new rules forbidding the use of drugs on racehorses within 24 hours before post time.

Meeting today in downtown Baltimore, the commission unanimously voted to ban the use of Butazolidin and Lasix beginning Monday, opening day at Bowie. "Bute" reduces soreness and swelling. Lasix is a diuretic.

In adopting the ban, the commission turned aside protests from Maryland horsemen who asked that moderate use of the drugs be allowed.

As the commission arrived at its decision, several blocks away in U.S. District Court an out-of-court settlement was reached in a civil lawsuit in which the heirs of a jockey killed at Pimlico two years ago argued the death was caused by excessive use of Bute on a racehorse.

In the last decade, the proliferation of drugs in the racing industry has become a matter of escalating concern. In Florida and Illinois, numerous trainers have been barred from racing for the illegal use of drugs.

In Maryland, one veterinarian was jailed for failure to keep proper drug records.

Racing experts generally agree that drugs used properly can be an aid to hard-working horses. But it is also possible for unscrupulous trainers to manipulate a horse's performance on the track through the use, or lack of use, of a variety of drugs that affect blood pressure and tolerance of pain.

The commission's firm stand today was in marked contrast to previous meetings at which horsemen were always able to forestall implementation of stringent drug regulations.

Fendall M. Clagett, president of the Horsemen's Benevolent and Protective Association, predicted the new rules would "slow down the entries at Maryland tracks.

"You're going to have a lot more five-and maybe even four-horse fields, said Clagett, adding that many owners would take their horses to Delaware and other states with more lenient rules.

"The commission made a grave error going from one extreme of unlimited medication to the other extreme of no medication at all," said Clagett. "These are therapeutic drugs, not narcotics."

Another horseman, H. Steward Mitchell, told the commission that he had a horse that had been treated with Bute and Lasix for years with no ill effects. The horse is still winning, he said.

Commission member Kenneth C. Proctor, Gov. Harry Hughes' only appointee to the commission and the spearhead of the drive to implement the new rules, said that "these rules are not written in stone."

They can be changed if they don't work, Proctor said, adding that there is wide discretion allowed the racing steards and the commission in imposing penalties for violations.

The lawsuit settled out of court today involved a jockey, Robert A. Pineda, 25, who was killed while riding in the second race at Pimlico May 3, 1978.

According to documents filed in the case, Paneda was astride a horse, Easter Bunny Mine, when another horse, Easy Edith, snapped a leg in front of him, and fell to the track.

Pineda's mount fell over Easy Edith. Pineda was thrown from Easter Bunny Mine and suffered fatal head injuries.

His widow's suit claimed that a large dosage of Bute was administered to Easy Edith by trainer Thomas S. Caviness shortly before the race.

The drug, according to the suit, "so insensitized Easy Edith's legs that she was unable to feel pain from injuries which she had prior to the race, which injuries would otherwise have been obvious to her, to her jockey and to other jockeys in the race, and which injuries should have precluded Easy Edith from running in the race."

Pineda's widow sued Caviness, three veterinarians, the owner of Easy Edith and the Maryland Jockey Club, which operates Pimlico, for $10 million, plus costs. All defendants shared in the settlement, but said they had made a pact not to divulge the terms. A source said it was "just under six figures."

One defendant, Ben Cohen, treasurer and part owner of Pimlico, said, "It was peanuts compared to what they asked." Ira Cooke, the lawyer for Caviness, said the settlement is not an admission of wrongdoing on the part of his client.

"Given the atmosphere today after the Preakness, it was better to settle," he said.

Implications of the settlement, according to racing experts, are broad and profound. They include the possibility that jockeys injured in the course of riding horses who have been given pain-killing drugs may have recourse to substantial financial damages.