FIVE-HUNDRED Maryland dogs were among the 1,650 purebreds that competed from early morning to late afternoon Sunday at the 79th Maryland Kennel Club's all-breed show at the Fifth Regiment Armory.
When the day was over, Peter the poodle from Potomac had done it again.
Champion Whisperwind On A Carousel, a 5-year-old standard poodle owned by Joan and Frederick Hartsock of Potomac, was best in show.
The absolutely beautiful poodle had also won the coveted best in show at last week's 115th Westminster Kennel Club show at Madison Square Garden in New York. His victory here gave him 230 group wins and was his 94th best in show. Last year he defeated 62,605 dogs and is the top winning male poodle in the breed's history.
And, he is just six best-in-show wins away from another record. Joan Hartsock says he is not being retired until he has won his 100th best in show, which should be within a month or two since the dog is being shown every weekend by his handler, Dennis McCoy, or Randy Garren, another handler, at shows around the country.
''The reason,'' says Hartsock, ''is that in the entire history of dog shows, only seven dogs have ever achieved 100 best-in-show wins, and we want Peter to reach that.''
The poodle is the first standard poodle the couple has owned. They purchased him from Linda Blackie, a friend and breeder who owns the Whisperwind Kennels in Altoona, Pa.
''He was an excellent choice,'' says proud Joan Hartsock from their Hartwyn Kennels in Potomac. ''I am a toy poodle breeder and have been for more than 10 years,'' she says. Her husband, Frederick, is a surgeon in Washington.
The Maryland win was another the shot in the arm for poodle fanciers, who had waited since 1973 for a poodle to take best in show at the Westminster. Poodle breeders also remember the drop in registrations with the American Kennel Club, where it had enjoyed top place from 1959 to 1984, when the cocker spaniel became No. 1 in registrations.
Hartsock says she will always remember the judge at a party in New York after the Westminster last week ''who told me that Peter is the finest specimen of any breed he'd seen since an English springer spaniel won the Westminster in 1963.''
Stud fees for a Westminster winner can be very high. It is said some breeders ask $2,000 or more. However, Hartsock says she isn't interested in cashing in on her winner and will use him only to improve the breed. His fee will be $700 and only to carefully chosen breeders.
The Maryland Kennel Club group winners on Sunday included some exceptional Maryland dogs. The group wins were:
* Sporting group. A beautiful black and tan Gordon setter, Ch. MacAlder Upland Hunter, from Carmel, Ind.
* Hound group. An Afghan hound, Ch. Casbar's Sugar-N-Spice, from Chicopee, Mass.
* Working group. A Doberman pinscher, Ch. Brunswig's Cryptonite, from Florida.
* Terrier group. A lively bunch, and first place went to a Welsh terrier, Ch. Sunspryte Gregmar Shorlyne, from Virginia. A Dandie Dinmont named Ch. Pennywise The Butler Did It, owned by a Marylander, Catherine B. Nelson from Potomac, was second.
* Toy group. A Maryland toy poodle, Ch. Hell's A Blazen Jazz Drummer, owned by Frances Rubinich of Indian Head, won first; a smooth coat Chihuahua, Ch. Bayard Breezy, owned by Diane Cox, Melanie Newell and William Miller from Baltimore, was second.
* Non-Sporting group. Best in show, Peter the poodle from Potomac, was first; a chow chow, Ch. Linnchow Maximillian, owned by Dr. Jo Anne S. O'Brien from Washington, D.C., was second, and a bulldog, Ch. Brumar's Call Me Higgens, owned by Sigrid J. Treat from Oxford, was third.
* Herding group. An imp of an Old English sheep dog, Ch. Whisperwoods War Lord, from Reisterstown, owned by Joyce Wetzler and Catherine Cargo, was first. A German shepherd who also has his Utility Dog obedience title, Ch. Banbury Cross Mikado, UD, owned by Gail Ladd of Westminster, was fourth.
* The Chesapeake Cat Club's 28th Cat Fanciers Association all-breed cat show will be held 10 a.m. to 5 p.m. March 9 and 10 at Timonium Fairgrounds. Entries will be taken through Feb. 24. Call Marie Surasky, 277-1214 days or 486-7548 evenings, or Madeleine Beck, 821-8127. Entry is limited to the first 450 cats.
* The Maryland Cocker Spaniel Club will hold its 52nd Specialty Show from 9 a.m. to around 5 p.m. on March 16 at the Charles H. Hickey Jr. School gymnasium, 2400 Cub Hill Road. For details of entries, which close Feb. 24, call show chairman Marion A. Bell, 821-9064, or Annette Davies, 592-9258.
* The Dog Owners' Training Club of Maryland will hold its 54th obedience trials from 9 a.m. to 6 p.m. on March 17 in the 4-H Building, Timonium Fairgrounds. For details of entries, which close Feb. 27, call Thomas H. Stromer, show chairman, at 747-0486.