For most of last year, trainer Shug McGaughey struggled to get a sense of Rhythm. The beat is barely more distinct as Rhythm composes for today's $500,000 Donn Handicap at Gulfstream Park.

Traditionally the first major handicap in the East each year, the Donn has added meaning today in that it touches off the American Championship Racing Series. The novel program, consisting of dirt races for older horses, will award $1.5 million in bonuses to the four horses who accumulate the most points over 10 races nationwide, most of them handicaps.

ABC will televise the Donn at about 5 p.m. as part of "Wide World of Sports" and follow it with the Eclipse Award announcements honoring the outstanding performers in thoroughbred racing during 1990.

Laurel and Pimlico will simulcast the Donn as the 11th of 12 races, preceded by the $40,000-added Dancing Count Stakes for 3-year-olds.

Rhythm is considered the one to beat in the nine-furlong Donn despite a season-opening defeat in the Creme Fraiche Stakes at Gulfstream two weeks ago.

He leads his 11 counterparts with $1.5 million earned, but the 4-year-old has been a source of puzzlement to his stable since he was the nation's top juvenile in 1989. Rhythm had surgery to correct a breathing problem early last year but won only two stakes races thereafter.

His overpowering victory in the Travers Stakes had many believing he had turned the corner, but a third-place finish in the Woodward Stakes -- his first against older horses -- and a poor outing as favorite in the Breeders' Cup Classic rendered those thoughts premature.

"You never know about this horse," McGaughey said.

Rhythm had a scintillating training session earlier in the week when he worked a half-mile in 46 2/5 seconds at Gulfstream, but McGaughey said he expects Craig Perret to have the colt well off the pace today. It's a manageable approach given the speed of Jolie's Halo, No Marker and Shot Gun Scott.

Jolie's Halo has the rail and an untainted record in four starts. The late-blooming 4-year-old, a product of Happy Alter's stable, is challenging such staid performers as Secret Hello, Killer Diller, Yonder, Primal and Mercedes Won. And Sports View comes into the race with three consecutive graded stakes victories in New York.

This could be a memorable day for Perret regardless of Rhythm's performance; the jockey can win his first Eclipse Award today on the strength of a record-tying 57 stakes victories last year. Gary Stevens, the leader in purses, and Pat Day also are contenders.

The Eclipse Award announcements following the Donn will include horse of the year, in which Criminal Type is expected to outpoint co-finalists Unbridled and the late filly, Go for Wand.

Maryland's Mark Johnston has a good chance to be named the champion apprentice, and Maryland-bred Safely Kept is a candidate for sprinter of the year.

Laurel's live feature, the six-furlong Dancing Count, reacquaints stakes winners Colonel Hill and Gala Spinaway in a six-horse grouping. Colonel Hill braced for the sprint with two bristling workouts and will race with Lasix for the first time. Suspension Upheld

The Laurel stewards announced King Leatherbury, the third-leading trainer in thoroughbred racing history, will begin a 15-day suspension today for the phenylbutazone overage in Wait for the Lady following a race at Pimlico in September. Leatherbury failed in an appeal to overturn the penalty.