The Potomac Stakes, Maryland harness racing's most successful race, takes place at Rosecroft Raceway tonight for the first time since its inception in 1982. It had been held at defunct Freestate Raceway.

Thirty-nine 2-year-old pacing colts have been entered in the $330,435 race, which has been split into four eight-horse divisions and one seven-horse division.

With the bulk of 2-year-old stakes yet to be raced this season, most of the colts entered in the Potomac have not had the opportunity to distinguish themselves. One exception is June's Baby, who won the $474,500 Sheppard Pace at Yonkers Raceway last week.

Driven by Ron Waples, June's Baby overcame the outside eight post on the half-mile track to win the Sheppard in 1:58 2/5 at 48-1 odds. His second victory pushed his earnings to $253,275, the highest among Potomac entrants. Waples gets the call on June's Baby again tonight.

Despite the Sheppard victory, June's Baby is not the morning line favorite in his division. Razzle Dazzlem, a Nihilator colt who showed remarkable gate speed in winning a race at the Meadowlands last week in 1:56, is expected to be the favorite. He will be driven by Eddie Davis.

Other divisional race favorites are Hello Almahurst, another Nihilator colt, who has won four of six starts for trainer-driver Roger Hammer; Deep Heat from the Ray Remmen stable, which also handles Beach Towel, currently the country's top-rated standardbred; Stormin Jesse, a winner last week at Rosecroft in 1:56 1/5 in the Baltimorean Series final, and Lefty, who has won in 1:55 3/5 this season, the best mark among the Potomac pacers.

When raced at Freestate, Potomac Stakes night generated a million-dollar handle four times, including a record $1,094,054 in 1984.