Jockey Herb McCauley agonized for days over what might be the most critical decision of his career. He had been riding both of Maryland's prime candidates for the Kentucky Derby, but he finally had to choose between the two.

After Saturday's Wood Memorial Stakes at Aqueduct, he should know whether he made the right decision.

Billy Boniface, who trains the talented 3-year-olds Deputed Testamony and Parfaitement, insisted that the jockey pick his mount so he could line up a rider for the other. Boniface planned to run Parfaitement in the Wood Memorial and Deputed Testamony in next Thursday's Blue Grass Stakes at Keeneland and then--if all went well--enter them both in the Derby.

"Herb called me three times from the Bahamas," Boniface said. "He said he was going to the cathedral and praying. Finally, he decided on Parfaitement." The trainer promptly got the services of Sandy Hawley, one of California's top riders, for Deputed Testamony.

McCauley has an excellent chance of getting a quick payoff on his commitment to Parfaitement. The colt looks at least as good as any of the other 18 colts who were entered in the Wood, necessitating its split into two divisions.

Parfaitement ran six times at Keystone Race Track last year, scoring six victories. He made his 3-year-old debut by winning a minor stake in Canada, then beat older rivals in a handicap race at Aqueduct last week. One of the horses behind him was Muttering, who had been the favorite in the 1982 Kentucky Derby.

Parfaitement's chief rival in the second division of the Wood, which will be run as the eighth race, is the unbeaten Megaturn, who has looked impressive in compiling a three-for-three record in New York this spring. But trainer Richard Nieminski said earlier this week that his colt was too unseasoned for this 1 1/8-mile test. Two days later, he changed his mind and entered him in the Wood.

Other major contenders in the lineup are I Really Will, Slew O'Gold and Jacque's Tip.

The first division of the Wood has drawn a distinctly weaker group of horses. The favorites are Country Pine, who finished eighth in the recent Flamingo Stakes at Hialeah, and Bounding Basque, runnerup in the Gotham Stakes at Aqueduct.

A New York Racing Association spokesman said the track was "not anticipating any real problems" despite a strike of maintenance workers. Mutuel clerks have been honoring the picket lines, but the NYRA has used administrative personnel to staff betting windows.