Thirty years ago this month on this picturesque course where the wisps of fog drift in on cue from the Pacific, a teen-age apprentice jockey named William Shoemaker led a horse race for the first time.

The remarkable career that followed came within inches of ending July 27 when a 3-year-old maiden filly named Proper Impulse stumbled badly leaving the gate and threw Shoemaker. The horses went by and Shoemaker lay, not moving, on the track. Old-timers here were reminded of a spill at Hollywood Park a decade ago that severely injured Shoemaker, sidelined him for more than a year and almost caused him to quit racing.

This time, however, Shoemaker bounded up and walked away.

"I was resting," he said, with a slight smile. He rode another mount to victory, and took the rest of the day off.

Shoemaker will be 48 this month. He is riding six days a week at Del Mar, usually five or six mounts a day. He says he is looking forward this fall to riding Kentucky Derby and Preakness winner Spectacular Bid in the East.

"No one ever rode a running horse the way Willie Lee Shoemaker does," sportswriter Jim Murray once wrote. "Not Geronimo, the James brothers, the Pony Expressers, the Buffalo hunters, the Lone Ranger, Paul Revere or the Headless Horseman of Sleepy Hollow. He is history's all-time calvalryman."

The record book supports this assessment. Shoemaker long ago passed Johnny Longden, who rode until he was 59, in the important statistical categories - most winners at 7,706, most stakes winners at 762, most victories in races worth $100,000 or more at 142. In his 30-year career, Shoemaker's horses have earned purses of more than $80 million. He still boasts his teen-age weight of 93 pounds, and is immensely proud of these achievements but says they are not the reason he continues to ride.

"The statistics don't mean a thing to me," Shoemaker said between races. "I'm out there every day because I enjoy it."

Shoemaker, who weighed 2 1/2 pounds at his premature birth - his doctor did not think he would survive - said he didn't realize how much he enjoys riding until his near-crippling injury in 1968.

"I missed riding so much," Shoemaker recalled. "If I hadn't been hurt, I might not have realized how much I enjoyed riding. I had a lot of time to think about it. It may have prolonged my career."

The other event which prolonged it, in the opinion of those who know Shoemaker, is his third marriage last year to Cynthia Barnes, 28, the daughter of an Army brigadier general.

"I feel better and my mental attitude is better," said Shoemaker, who proved it by going on a winning tear at Santa Anita soon after the marriage.

But the reviews on Shoemaker's riding at the current meeting at Del Mar, a celebrity-conscious track founded by Bing Crosby, Pat O'Brien and other Hollywood figures in 1937, have been mixed.

For the top jockeys and trainers in Southern California, the 43-day Del Mar meeting is a pleasant interlude after the hard grind of Santa Anita and Hollywood Park. The weather is mild, the atmosphere relaxed, the horses cheaper. Because many 2-year-olds make their debuts here, Del Mar sometimes is called the "Saratoga of the West." But Shoemaker is the first to say that few of the horses are of Saratoga caliber.

"He is riding not good, not bad, just taking it easy and giving a professional minimum," said one experienced horseman, who is usually a Shoemaker admirer.

But there is another view, shared by Shoemaker, which is that the veteran jockey is riding as well as he has in the past decade. Except for the undefeated Parsec, many Shoemaker horses at Del Mar have been either long-price claimers, first-time starters, or both. And Shoemaker has been getting many of them home in the money.

The other day Shoemaker scored a $35.20 victory aboard a $16,000 claimer named Bronze Bobbie, not exactly the kind of premium horse Shoemaker is famed for getting under the wire. Other jockeys say Shoemaker still is unsurpassed in longer races at possessing a sense of pace and of knowing where he is on the track at all times.

Shoemaker says the annual stress tests show him to have the body of a 25-year-old. And while not many would compare the Shoemaker of today to the Shoemaker of 25, he undoubtedly is riding better than he was in the mid-1970s, when for a time he was overweight and seemed on the decline.

Now, the 4-foot-11 jockey seems much like the Shoemaker of old. He is tanned, polite, composed, a little grayer. In the mornings he plays tennis near the beach and sometimes, before the races, plays cards with the other jockeys. On the track, his stirrup is shorter in the manner of modern riders - "a better style," Shoemaker calls it.

At 48 he still looks forward to more victories, to the dream of the Triple Crown he has never won (despite three Kentucky Derby victories) and to riding Spectacular Bid, whenever and wherever he runs.

The bit jockeys love big horses, and Shoemaker was delighted to replace Ronnie Franklin aboard Spectacular Bid.

Diplomatically, Shoemaker refrained from saying he would have won the Belmont Stakes and refused to criticize Franklin. Some of Shoemaker's friends say the switch of jockeys has put a certain measure of pressure on Shoemaker, who could be unfavorably compared to controversial apprentice Franklin if he doesn't win.

If Shoemaker feels this pressure, he doesn't show it. His emotions are controlled, deep inside him, as they were that day when he strolled back into the jockeys' room and prepared for a victory after his spill.

"I look forward to riding Bid. I really do," Shoemaker said. "It's a helluva opportunity. I'll be ready when he is." CAPTION: Picture, Willie Shoemaker