The contestants are prepped and primped, sometimes for as much as $250,000, as if they were models getting ready to sashay down a prestigious runway.

They are models of a sort - four-legged ones, anyhow (that's twice as much sashaying) - and the runway is one of the most prestigious in the United States, if you are a dog, or a human owner, breeder or handler of one.

The Kennel Club of Philadelphia's annual National Dog Show Presented by Purina takes place this weekend at the Greater Philadelphia Expo Center at Oaks. The recorded broadcast, aired nationwide on NBC on Thanksgiving Day, has become a holiday tradition, sandwiched between the Macy's Thanksgiving Day Parade and football.

More than 20 million viewers tune in every year to see about 2,000 purebred dogs representing 170-plus breeds from throughout the country compete for the crown of best in show. Residents in the Philadelphia region can visit the show on Saturday or attend Sunday to see additional dog exhibitions and participate in activities geared toward both children and adults.

"It's a wonderful way for families to spend a day," says actor John O'Hurley. Probably best known for his role on TV's Seinfeld as clothier J. Peterman, he's gaining fame as TV host for the National Dog Show.

David Frei, communications director for the Westminster Kennel Club and "the dean of dog show commentators," has sat beside O'Hurley as the expert analyst since the Philadelphia show's first national broadcast in 2002. The Kennel Club of Philadelphia has been holding dog extravaganzas for more than 125 years.

What makes the National Dog Show so family-friendly is also what makes it rare: It is one of five remaining dog shows in the country that are benched. In pooch parlance, that means the dogs and their humans remain backstage at the show all day, before and after their individual competitions. The public can walk up to the dogs, take a close look at them (and maybe pet them), and ask questions of the handler.

"If you're looking for a dog, it's a great place to go," says O'Hurley, who owns a Cavalier King Charles spaniel named Sadie and a Havanese named Lucy.

It helps to understand the judging criteria for the dogs, which this year include two new breeds the American Kennel Club has qualified to participate - the Russell terrier and the Treeing Walker coonhound.

Specialized kennel clubs, Frei explains, write standards for each breed's ideal specimen. Canine contestants are judged against these standards. So Labrador retrievers are compared to the ideal Labrador retriever, cocker spaniels to the ideal cocker spaniel, and so on.

Dogs first compete within one of seven official groups, such as herding dogs, hounds, and terriers. The champion of each group then competes for best in show, based on appearance, physical structure, and behavior - again, as compared to its own breed's standards.

Last year's overall winner was a fit and regal-looking wire fox terrier whose friends call him Eire.

Chester County's Margery Good has shown dogs in the local show since the 1970s, and she will again this weekend. Good, 60, is a professional dog handler and owner of Goodspice Kennel in Cochranville, which specializes in breeding Sealyham terriers. One of her Sealyhams took home the top prize in 2006, she says.

She says judges examine each dog for such qualities as bone structure, musculature, alignment, number of teeth, placement of ear and eye, quality of coat, and length between last rib and back legs. All these are compared to that breed's ideal standards.

The challenge for handlers is to keep their dogs looking alert and at their best at all times, in case a judge takes a second glance.

The best part of showing a dog, Good says, is when the handler gets "a feeling of cooperation with that dog, when you ask them to put on their very best performance and they do it and the judge sees that and loves that dog."

Sometimes, it seems, dogs judge the humans.

O'Hurley has a pungent memory of one National Dog Show years ago. A Great Dane walked by the broadcasting booth, stopped in front of it, looked at him and Frei - then squatted and "left a sizable critique for us," O'Hurley says.

He laughs over the phone, and admits he has his favorite breeds. He yearly roots for an Irish setter to win.

When it comes to watching the show at home on Thanksgiving Day with loved ones, Frei says, there really should be only one favorite for champion canine.

"The real best-in-show is the dog on the couch sitting next to you," he says. "So hug your dog."

Putting on the dog

What: The Kennel Club of Philadelphia's National Dog Show Presented by Purina.

Where: Greater Philadelphia Expo Center at Oaks, 100 Station Ave., Oaks.

When: Saturday from 8 a.m. to 6 p.m. and Sunday from 8 a.m. to 5 p.m.

(On Saturday, in addition to taping the audio for the broadcast, John O'Hurley will hold a book signing and David Frei will be available to talk with the public and dog owners.)

Admission: Adults 12 and over, $14; children 4-12, $7; children 3 and under, free.

TV: NBC10 Thursday, noon to 2 p.m., after the Macy's Thanksgiving Day Parade.