Seattle Slew, the overwhelmingly early favorite for the Kentucky Derby, makes his first important start of the season Saturday in the $139,400 Flamingo Stakes.

Trainer, Billy Turner Jr., promises the performance will be "something to see . . . a race to remember. Seattle Slew will handle the mile and an eighth better than his shorter races."

If he does, the Hialeah fans and national television audience (5 p.m., WMAL-TV-7) are in for a treat, because Seattle Slew has been sensational in the last two starts of his short but brilliant, undefeated career. The dark bay colt won the Champagne Mile in Belmont's Park in October by nearly 10 lengths in a stake-record 1:34 2/5, then scored by nine lenghts here March 9 in seven furlongs in a track record 1:30 3/5, eased up.

He is 4-for-4 and untested with the Kentucky Derby at Churchill Downs May 7 only three races away.

This morning, shortly after 6 o'clock, Seattle Slew blew out three furlongs in :37 for exercise boy mike Kennedy. Last season's champion 2-year-old does not breeze very often.

"He reminds of a Never bend, an extremely rapid horse which I used to train short, like Turner does with his horse," Woody Stephens noted.I never worked North Bend harder than five-eights of a mile, so I readily understand Turner's methods with Seattle Slew. By the time you've slowed down a fast horse, he's gone far enough."

Never Bend was a particularly quick, talented runner which won the 1963 Flamingo and finished second to Chateau gay in Louisville. Seattle Slew has run faster than Never Bend or anything else, except, possibly a cheetah, up to this point. Small wonder then many horsemen are convinced he will go from the Flamingo to a greater glory just as Citation, Tim Tam, Carry Back and Northern Dancer did in the not-too-distant past.

Twelve other 3-year-olds are set to oppose Seattle Slew Saturday. They are, in post position order: Wine Treasure, Jatski, True Statment, (Seattle Slew), Fort Prevel, Marcho Hombre, Sir Sir, Iron Constitution, Coined Silver, Ruthie's Native, Pepelote, Giboulee and Caviar Kid.

All starters will carry 122 pounds. Ruthie's Native and Coined Silver captured the divisions of the Florida Derby at Gulfstream Park early this month. Most of the others lack credentials except Fort Prevel and Sir Sir , a lightly race Sir Ivor colt which finished well in the second half of the Florida Derby.

Wine Treasure, a 110-to-1 shot at Gulfstream, is something of an outlaw horse. His nomination to the Tripple Crown races was turned down because of his allegedly "hidden" ownership.

There is some speed in this Flamingo, Ruthie's Native, for example, but none has the exceptional early firepower of Seattle Slew, and Turner is not coy about strategy.

"Never take a good horse back to a bad horse," the 36-year old trainer said. "If you're in front, and going easily, don't worry about the others."

Seattle Slew never has known what it's like to be behind for long, not even in his second start when he was nearly left at the gate.

"He's been so much the best there's been no way to know exactly," said Frenchman Jean Cruguet, his regular rider, "If the others come to him at the head of the stretch, as For The Moment did in the Champagne, I expect Seattle Slew to take off again. If he doesn't, I'll be sick. This colt is quicker, more willing than Hoist The Flag, and the quality is the same."

Seattle Slew is a son of a deceased sire, Bold Reasoning, out of a Poker mare. Bold Ruler and Round Table are great-grandsires on the top and bottom of his pedigree.

Dr. James Hill, a veterinarian, selected the colt for Karen and Mickey Taylor out of the Fasig-Tipton Kentucky Yearling sale. The price was $17,500.

"He was big and gangling, like the big kid on the block, and accordingly he was a little behind the other horses. They called him 'Baby Huey' on the farm," Dr. Hill recalled. The Taylors, a young couple from White Swan, Wash., (population 600), near Seattle, named the colt for their home area and for the swamplands near Dr. Hill's home in Fort Meyers, Fla.

Seattle Slew was broken by Turner's wife, Paula, on their farm in Monkton, Md.

Barn D. which like all others in the backstretch, here, is sadly in need of paint is where Seattle Slew is stabled. The grounds still make an attrative home for a young horse, however and for the large gallery which follows this colt's every move.

"It's like looking at a railway track," Dr. Hill said in describing Seattle Slew's conformation from behind. "His front shoulder is perfect and he has a straight hind leg. His pasterns and cannon bones are short. He has a great forearm (from the knee up).

"His disposition is perfect. I'd say he's walking taller every day.

"Most important, he has a wonderful, floating way of going. Once he gets in stride, I think he'll run all day."

Taylor concurs in that opinion. If they're right and the longer distances pose no problem, Seattle Slew could be as "memorable" as the trainer promises he will be in the Flamingo. The stake record is 1:46 4/5, set by Honest Pleasure last winter.