Ten Keys, a locally owned thoroughbred reported stolen two days ago, was found yesterday about 45 miles from the California stable from which he disappeared.

According to San Mateo police, Ten Keys was discovered by his owner, Charles Linhoss of Alexandria, and a California Horse Racing Board official at the Alameda County Fair in Pleasanton. The colt, one of Maryland's top homebred 3-year-olds, was returned to Bay Meadows race track in San Mateo, from which he was taken.

The CHRB yesterday received a lead from an unidentified trainer at Pleasanton who found a dark bay colt matching Ten Keys' description in his barn. Police had issued a description of the colt to state race tracks after his disappearance Saturday.

Police are investigating the case as a possible grand theft and are searching for the person who transported the colt to Pleasanton. However, Lt. Ed Smith, an investigating officer, said the case could be a matter of mistaken identity.

At about 10:45 p.m. Saturday, Bay Meadows stable superintendent Frank Goodwin discovered Ten Keys missing. A departure card, required for any horse leaving the stable area, identified the horse as Peruvian Blade. Peruvian Blade, who ran in Saturday's fourth race at Bay Meadows, was in his stall Sunday morning.

One man in a tan pickup truck with a small horse trailer was seen driving from Bay Meadows shortly after Ten Keys disappeared. The trailer was found yesterday at Pleasanton, police said.

Ten Keys, reportedly insured for about $1 million, was shipped from Maryland to California for the Nov. 22 Hollywood Derby at Hollywood Park. From there, he went to Bay Meadows, where he finished third in Saturday's Tanforan Handicap.

The colt had become a story even before he left Maryland. He was bred by Richard Bendit, a plumbing contractor from Ashton who retained ownership until Jan. 20, 1987, when trainer Michael Pino claimed the colt for Linhoss at a cost of $14,500.

Bendit denounced the claim, alleging that an exercise rider of the colt's former trainer, Bill Boniface, informed Pino that Ten Keys might be worth pursuing.

Under Pino's care, Ten Keys became one of Maryland's finest 3-year-old turf horses. He won five stakes races from May through October and has earned more than $200,000 for Linhoss.

Bendit denied any part in Ten Keys' disappearance. "I don't operate that way," Bendit said. "It's frustrating, and I'm still emotional, but I wouldn't do such a thing as steal the animal."

Neither Linhoss nor Pino could be reached for comment.