Just 10 days ago, the outlook for the Kentucky Derby seemed utterly inscrutable. None of the country's 3-year-olds had displayed exceptional ability; dozens of them had the potential to win at Churchill Downs in a weak year.

But after the past week's prep races, the whole picture has suddenly become clear. Still no exceptional horse has appeared anywhere, but a superior group has emerged: the group of 3-year-olds based in California.

All the evidence suggests that a colt from the West will be triumphant on the first Saturday in May.

This conclusion causes me some embarrassment. Having spent 11 weeks at Santa Anita this winter, I did not think I saw any strong Derby candidates and did not even bother writing about the stakes for 3-year-olds. "Just a bunch of bums out here," I assured the boss.

In fact, there were so many capable 3-year-olds at Santa Anita that no individual was able to dominate the competition and thus look especially impressive.

But the quality of the colts there did not become apparent until they started running against rivals in different sections of the country.

* Croeso, who couldn't win a stakes race in the West, won the Florida Derby against the best 3-year-olds in that state. Two colts he beat, Current Hope and Chumming, ran one-two in Saturday's Flamingo Stakes at Hialeah.

* Marfa, who had won only a maiden race in eight starts in the West, went to Latonia and won the $200,000 Jim Beam Spiral Stakes by eight lengths. He trounced Noble Home, who was probably the best 3-year-old in Maryland this winter, as well as a number of the better colts from New York.

* Balboa Native, who had finished a distant third in one stakes appearance at Santa Anita, went to the Fair Grounds and won the $200,000 Louisiana Derby, beating the best 3-year-olds in that part of the country.

While these races demonstrated California's overwhelming superiority, last week's San Felipe Stakes at Santa Anita seemed to confirm the identity of the best 3-year-olds in the West.

Naevus battled head-and-head all the way around the track with Desert Wine, lugged in badly through the stretch drive and was in front by a head, only to be disqualified.

The two of them finished nine lengths ahead of some formidable competition, and the time of the race was excellent.

The cognoscenti at Santa Anita aren't sure whether Naeveus or Desert Wine is the better horse.

They point out that Naevus was getting a nine-pound weight concession from his rival, but also say that he would have won clearly if he had kept a straight course. The Santa Anita Derby on Sunday should settle the issue.

That will be the key prep race for the Kentucky Derby, because the number of legitimate contenders elsewhere is small and steadily shrinking.

The New York contingent lost its only potential star when undefeated Strike Gold was sidelined by a minor physical problem last week.

The only Florida-based colt who hasn't repeatedly proved his mediocrity is Pax in Bello, who is expected to run in a stakes race later this week.

It was only a few years ago that students of the Kentucky Derby looked with skepticism or condescension on any horse from California; even horses with overpowering records had to prove themselves east of the Mississippi before they could be taken seriously.

Now the opposite is true. No matter how unexceptional a Derby candidate's record may look, he deserves some attention if he is coming from California.