There are few mysteries surrounding the Preakness.

Spectacular Bid will be meeting four horses whom he defeated convincingly in the Kentucky Derby two weeks ago. With no new challengers, he justifiably will be one of the shortest-priced favorites in the history of the Pimlico classic.

But there may be a significant difference between the Derby and the Preakness: the way the early stages of the race are run. And that difference gives General Assembly his one hope of springing an upset: by opening such a big early lead that the favorite cannot catch him. It is not likely, but it is conceivable.

Pimlico is a track that habitually favors front-running horses. Bettors here learn quickly to upgrade the chance of any horse who figures to get a clear early lead.

General Assembly has the speed to take such a lead Saturday if jockey Laffit Pincay permits him. He demonstrated his quickness before the Kentucky Derby when he worked five-eighths of a mile in 57 2/5 seconds, though in the race itself Pincay did not employ that early speed. He put General Assembly under wraps as he came out of the gate, although he found himself running head and head for the lead because there was no speed in the field.

General Assembly showed on Wednesday that he still has his quickness, working five furlongs in 58 2/5 over a dull Pimlico strip. After that move, trainer LeRoy Jolley was asked if the colt would use that speed early in the Preakness.

He equivocated. "It's up to Pincay," Jolley said. "It was his option in the Derby, and it's his option here."

If Pincay does decide that he wants to try to steal an early five-length lead, none of the supporting cast in the Preakness field can stop him. Golden Act is a confirmed stretch-runner. Flying Paster never has been an early lead in his life. Screen King has shown little speed in his recent starts.

Which leaves Spectacular Bid as the colt who is going to have to pursue the leader. Trainer Bud Delp knows this. "I won't be concerned as long as we're laying second," Delp said. "I want my colt to be on General Assembly's tail."

He made an effort to sharpen Spectacular Bid's speed when he worked him three eighths of a mile in a swift 34 seconds this morning.

But it remains to be seen how close to General Assembly's tail Spectacular Bid can get. Spectacular Bid had abundant speed as a 2-year-old, leading in some of his races from wire to wire, but he is a different horse this year. Delp has trained him for stamina instead of speed, giving him two-mile gallops most every morning and few short, sharp workouts.

As a result, Spectacular Bid does not have the quickness that he used to. In the Blue Grass Stakes at Keeneland, Delp told jockey Ronnie Franklin that he wanted the horse to show speed from the start. Franklin was pumping as soon as the gate opened, but when he hit the turn Spectacular Bid was last in the four-horse field.

If Spectacular Bid does not have the speed to press the leader in the early stages of the Preakness, General Assembly will posses an edge he did not have in the Derby. The question is whether that edge is significant enough for him to beat Spectacular Bid. The answer is: Probably not.

While Spectacular Bid beat General Assembly by 2 3/4 lengths in the Derby, that margin may not fully reflect the extent of his superiority over his rival. He lost at least a couple lengths on the turns because of Franklin's inelegant ride. And he might have been able to run faster if he had been pressed.

Although the Derby represented General Assembly's maximum performance, Spectacular Bid has run better races in Florida than he did in the Derby, and he might be able to reproduce them if he has to.

So, unless General Assembly can steal off to a huge early advantage, and Franklin rides a race that is terrible even by his standards, Spectacular Bid should be able to spot the front-runner an early lead and run him down.

The order of finish in the Preakness should be a rerun of the Derby; Spectacular Bid, General Assembly and Golden Act. CAPTION: Picture, Kentucky Derby Runner-up General Assembly gives a horse laugh to his exercise rider, Ron McKenzie, prior to workout. UPI