The Thoroughbred Board of Maryland's Racing Commission has asked the state attorney general's office to investigate charges that three of the state's leading trainers have agreed not to claim each other's horses in claiming races.

In a 4-to-0 vote, the board called for an investigation into charges of collusion by trainers King T. Leatherbury, Richard E. Dutrow and Richard W. Delp.

The board acted following publication of stories in the Baltimore Evening Sun that said state records indicate the trainers did not take any horses from each other during 1980.

For several years, critics of Maryland racing have complained that the three trainers appeared to have an unofficial agreement not to claim each other's horses. Asked about this, Leatherbury once said that every trainer has friends and colleagues from whom he will not claim horses. That is simply track etiquette, he said.

However, Maryland law specifically prohibits trainers from entering into advance agreements not to claim each other's horses during claiming races.

"If the allegations about the claims are true, it's a violation of the rules," said board Chairman Robert W. Banning.

A claiming race entitles any licensed trainer to claim any horse in the field for a prefixed price, usually ranging between $3,000 and $25,000. Thoroughbred tracks in Maryland usually run five or six claiming races a day. t