Two weeks ago, Ken Singleton looked at his right hand and noticed "it was half the size of the left." A nerve problem--"I wish I could tell you medically exactly what it is"--had weakened his hand and his hitting. "I went and got tested," he said. "They said it was 15 percent weaker than the left."

In the last two weeks, Singleton has been doing exercises and raising his batting average from .249 to .275. Today, he hit a three-run home run to beat the Seattle Mariners, 4-3.

Afterward, he was explaining how much stronger he feels. A little boy visiting the locker room gazed up at the man in the "Maryland Hit 29" T-shirt and said incredulously: "How much stronger can he get?"

Singleton doesn't really want to know. It is enough that he feels he has an explanation for the difference in his left-handed hitting (.302) and right-handed hitting (.190) this year, between the first half of 1981 (.340) and the second (.209).

"I haven't been back to ask how much strength I've gained," he said. "I don't want to know that. I don't want them to tell me it's still 12 percent weaker. I don't want to feel psychologically weaker when I go to the plate."

Anyone could have been forgiven for feeling a bit weak today. "Sultry was not a good enough word to describe it," the Oriole pitching coach, Ray Miller, said.

With two outs in the fourth, starter Jim Palmer capitulated to some well-placed hits (five of them) and to the steamy weather. Replacement Sammy Stewart gave up one hit and one walk and won the game. He has a victory and a save, pitching 6 2/3 scoreless innings, since returning from the minors on Thursday.

"He stopped us cold," Manager Rene Lachemann of Seattle said, an odd way to describe anything that happened today.

"It's easy to get loose," said Stewart, making the best of it. "Loose as a dishrag."

Palmer had six strikeouts in four innings (to tie his season high) and threw at 86-87 mph (also a season high). But "having to pitch with a man on third in the first and with bases loaded in the second, maybe took a little bit out of him," Miller said.

In the fifth, with the Orioles leading, 4-0, Palmer gave up consecutive singles to Todd Cruz, Bobby Brown, Manny Castillo and Bruce Bochte, a sacrifice fly to Al Cowens and another RBI single to Richie Zisk. Suddenly, it was 4-3.

Manager Earl Weaver, who did not want to do it, came and got Palmer. "It's not like they were crushing him," Weaver said. "It's just now the ground balls are going through the infielders and the fly balls aren't getting to the outfielders."

Stewart came in with two outs and got Dave Henderson to bounce to short for a force at second. On Thursday, he saved a 4-3 victory for Scott McGregor and today he won one.

Stewart, who had been starting before his knees went bad, says, "I'd kind of like to keep doing this job."

If he sounds laconic about his changing role (he probably will get some spot starts with five doubleheaders coming up), then Singleton sounds resigned. This year he has become a full-time designated hitter (he's played the outfield only twice). He says he'd rather have it this way than "bouncing back and forth."

The Orioles were leading, 1-0, in the third. Loser Mike Moore had walked Al Bumbry and Glenn Gulliver (he has been on base six times in eight major league at bats since arriving from Rochester Friday). The count was 0-1. Moore threw Singleton a changeup, the only one he saw all day.

He stood at home plate and saw it head for the right-field stands. He ran a bit, stopped at first, saw it clear the fence (his 47th, 48th and 49th RBI, one less than Eddie Murray), and headed for home.

"I didn't think it was going out," he said. "I looked at the flags (the wind was blowing out). Sometimes, you gotta go with the elements."

Cowens made a mistake, Singleton explained, playing the corner they called "Ken's Korner" for so many years. "I don't get a chance to make that mistake anymore," he said. Quickly, quietly, he said that doesn't bother him anymore. Too quickly perhaps.

"He went back and got too close to the wall," he said. "You can't jump because the ball's right at your back, you get into it. If you drift, drift, you can't jump."

Would he have caught it? Singleton smiled. "I would have reached, angled my body. Who knows. If I was hitting it, I wouldn't have."

It remains to be seen whether Weaver will be fined or suspended for apparently making contact with umpire Terry Cooney in a confrontation Saturday night.

Asked if he made contact with the umpire, Weaver said: "More than likely I did. But I'm not blaming him so I hope he doesn't blame me. If there was (contact), I forgive him."

Said Cooney today: "I don't want to make any comment until after I talk with (AL President) Lee MacPhail."