Laurel Race Course changes its post time to 12:45 p.m. starting today in hopes of accommodating the extra two races (the seventh and ninth) that will be simulcast from Aqueduct as part of the Breeders' Cup. There will be win-place-show betting on the two extra races with the seventh race, the Breeders' Turf Cup, being the final part of the Pick Six wagering.

Also, the layoff of security guards at Laurel has prompted the resignation of the union shop steward, Doug Bird.

Bird, a veteran of 15 years at the track, said, "I'm heartsick . . . some of the men that were let go were within a year of getting their pension from the track."

Since track management began asking all security guards to undergo stress testing last month, at least 14 of the normal complement of 33 guards have been laid off.

Laurel co-owner Tom Manfuso said, "Yes, we have trimmed our staff . . . but we have fulfilled our promise to those guards that could not pass the stress tests to offer them work on the backstretch. We are not insensitive to their pension status."

Towners Big Guy heads a field of five 2-year-old pacing colts in a Breeders Crown Preview at Rosecroft Raceway tonight. Rosecroft will play host to the Breeders Crown division for 2-year-old colts Nov. 8. The estimated $650,000 purse will make the Crown the richest horse race in Maryland history.

Rosecroft said it will hold the $200,000 Colonial Trot for 3-year-old trotters and the $60,000 Cradle of Liberty for fillies in the fall of 1986.

Pimlico Race Course has been criticized for not revealing its plans for the $3.5 million granted it by the state legislature this year. The criticism came in a report released today by the commission appointed by Gov. Harry Hughes to investigate the impact of professional sports on Maryland's economy.