In the tough business of claiming racehorses, there is not much room for sentiment.

Trainers may rhapsodize about the virtues of tough old competitors who keep winning in the lower echelons of the sport. But even for Port Conway Lane, who is 13 years old, who has a tumor on his head and who recently scored the 50th victory of a remarkable career, the bottom line is still dollars and cents.

Port Conway Lane has displayed every important equine virtue: class, consistency, gameness. If he were not a gelding, he would have been retired to a comfortable life at stud long ago. Instead, he has been asked to display one more importantquality: durability. He has been campaigning steadily since 1971, with only one six-month vacation in all that time, running 227 times and earning $421,691.

Trainer King Leatherbury couldn't have imagined that he was acquiring such a rare type of animal when he paid $7,800 for the son of Bold Commander at a yearling sale. Nor did Port Conway Lane look exceptional when he finished third in the first start of his career on June 30, l971, and then went on to score his maiden victory at Timonium that August. Although he soon established himself as a solid allowance-class horse, he didn't fully bloom until he was 5.

During one streak in 1974, he scored four straight victories by margins of a nose, a head, a nose and a nose. "He'd always get up in the last couple jumps," Leatherbury said. "That got to be his style." He won one stakes race that year, and two more the next season, competing against horses who will evoke vivid memories for Maryland racing fans: Leematt, Icecapade, Roanoke Island. All of them were retired long ago and were sent to stud. But when Port Conway Lane could no longer win stakes, he was dropped back into allowance company, and when he could no longer win allowances, he entered the claiming ranks in 1977.

If he didn't have the same ability, he still had the same competitiveness, and he was a desirable property for a claiming trainer. Trainer Marvin Kuhn took the gelding from Leatherbury in 1978, and a year later Leatherbury took him back. Kuhn claimed him again and Leatherbury took him back again. Then Port Conway Lane was claimed by another trainer, and after spending his whole career in Maryland he got to see the world. Evidently, he didn't like it. He campaigned in Florida last winter and couldn't even win for $5,000. But when he appeared in a $5,000 claiming race at Monmouth Park last summer, Leatherbury took him back.

Even though the gelding was 12 years old, Leatherbury said, "He was still sound. He always had a lot of energy and pep and he still had it. He was still a little sassy. The only thing wrong with him is a lump on his head. The vet says it's a tumor, but it doesn't seem to be growing too much and it's not bothering him."

Leatherbury's claim was motivated a bit by sentiment, too. "I really took him to get to 50 wins," he said. "I figured that if he should do it, it should be in our barn. If somebody else got it, I'd be jealous."

On Nov. 24, in a $5,000 claiming race at Laurel, jockey Bill Passmore brought Port Conway Lane from off the pace, moved on the turn and scored a half-length victory that was the horse's 50th. There is no official recognition for the feat -- it is a widespread misconception that such horses get a niche in the Racing Hall of Fame -- but it is a very rare feat, nevertheless.

One week later, Leatherbury ran the gelding for $5,000 again, and was stunned to learn that he had been claimed, by Marvin Kuhn. "I was shocked and a little bit saddened," Leatherbury said, "but we're basically a claiming outfit and it's ridiculous to cry over losing a horse. Everybody's been cussing Kuhn, but he had every right to take him."

Why did Kuhn buy a horse who will be 14 years old next month? Not for reasons of sentiment.

"This is the third time I've claimed him," Kuhn said. "When I had him, I ran him 38 times and won $45,000 with him. My plans for him are the same as Leatherbury's: to keep running him and try to make money."

Port Conway Lane will, assuredly, keep on running as long as he can make anybody money. Regardless of his past record or his admirable virtues, there are no rolling green pastures in the future of a cheap claiming horse.