A hitter's wind was blowing out of Candlestick Park. But that was the least of Kelly Downs' worries as he stood in front of his locker in the clubhouse of the San Francisco Giants. He wore a huge bag of ice on his right shoulder, locked in place by an ace-bandage harness.

"I'm a competitive person," he said, slowly moving the shoulder back and forth. "I love to compete. I want to pitch. I always want to pitch."Such was his motivation this past week at Candlestick when he took the mound against the Chicago Cubs even though he shouldn't have. Downs had felt some soreness in his shoulder in warmups, the same soreness he'd felt at the end of his most recent previous outing in St. Louis. He ignored it. Fourteen pitches, two walks and an error later, the bases were loaded with Cubbies and Downs was calling the bullpen for a getaway car.

"It was stupid, what I did," he said. "I loaded the bases. I hurt the team. But I didn't know what was going on and I had to find out."

What he found out was that as soon as he cocked his shoulder he experienced a major bolt of pain, enough to render his usual repertoire of pitches - headlined by a split-fingered fastball - mostly harmless.

"The funny thing," said Downs, hardly meaning funny in the conventional sense, "is that the shoulder feels fine, perfectly normal, until I cock it."

The trouble is, he has to cock it to throw a pitch.

On Friday, the Giants placed him on the 15-day disabled list, retroactive to May 2.

"It's frustrating," said Downs. "That's the word. Frustrating."

It's especially frustrating because Downs, the Viewmont High School graduate, just barely turned 28 years old, and, as far as pitchers are concerned, prime-time doesn't get any closer than this. After seven long (and mostly frustrating) years of minor league baseball, from 1980 through 1986, he finally got fulltime big league service the past two seasons. He went 12-9 in 1987 for the Giants, helping them to the NL West title, and 13-9 a year ago.

This year is supposed to be his year. He was projected to lead the Giants' staff along with 39-year-old veteran Rick Reuschel. He started off strong, winning his opener against San Diego (and fellow Utahn Bruce Hurst). He looked every bit a Cy Young Award winner possibility, as prognosticated by Sport Magazine's preseason baseball issue.

"I liked seeing that," said Downs of the magazine's prediction, "it's always nice to see that someone recognizes that you have the potential."

But, still, he knew he wasn't pitching at full strength as the season began. Ironically, it may have been overzealous conditioning in the offseason that was the problem. Some of the exercises he was doing with weights were pinching his right shoulder. He ceased and desisted when he realized what was going on, but not until damage had been done.

The shoulder that had stood him well through 27 years first acted up late last summer, when inflammation forced Downs onto the 15-day disabled list for the first time in his professional career. The problem then was with the muscles that slow the arm down after delivery.

This latest calamity is on the other end of the motion - dealing with the cap of the shoulder and the initiatory muscles of the pitching delivery.

Downs can do virtually anything he wants - household chores, heavy lifting, mowing the lawn, golf, even exercises in the weight room. With one exception. He can't pitch.

That's the bad news. The good news is that it should only be temporary. Examinations and x-rays of the shoulder this week revealed no tears or breaks on the inside, and, in general, revealed what Dr. Gordon Campbell, the Giants' team physician, termed, "A surprisingly clean joint."

"That was encouraging," said Downs. "I just have to be patient. I have to give it time. And I have to see what I might be doing to aggravate the situation. One thing that might help is I need to stop sidestepping on my stretch, and go quicker to homeplate. That should lessen the strain on my shoulder."

He will miss at least one turn in the rotation, and isn't scheduled to pitch again until May 17 in Philadelphia.

Downs said he can't wait; and neither can his manager, Roger Craig, who has great hopes for his 6-foot-4 righthander.

"Every year, I think Kelly Downs can win 20 games for us," said Craig. "There's no pitcher in the league I'd rather start. He's a good athlete, he can pitch well, and he handles the bat real well. We need him in there."