Americans are expected to spend $3 billion or more on Christmas for their pets this season — that's billion with a "b."

But what's really staggering is the ever-expanding variety of wacky, clever or just over-the-top stuff you can do for Fido, Fluffy and their brethren for the holidays.

As if they care it's Christmas!

The thinking nowadays: If people like it, pets will too — and especially dogs. In fact, more and more, dogs are being treated as if they were four-legged children. So you can take your dog to a spa for a massage or a manicure. Get his portrait painted. Take him to see Santa at the mall. Send his photo in Christmas cards to his doggie friends. And the gifts you can get him are, well, like the gifts you get a person. Handbags for cats. Couture for dogs. Bling for dogs. Daybeds for dogs.

Even Bob Vetere, president of the American Pet Products Manufacturers Association, says he's "flabbergasted" at the flood of goodies produced for pets — or, more accurately, for people who like to think their pets know it's Christmas.

"As a large chunk of the baby boomers are reaching empty-nester stage, they're turning to pets to fill the void," Vetere says. "They're tending not to reward pets in pet terms but in human terms — they're making themselves feel good by rewarding their pets in ways that are meaningful to them."

At PetSmart, the national chain, they call the customers — that is, the ones with the credit cards — "pet parents." Rashell Cooper, the dog fashion expert for PetSmart, says retailers are responding to consumers' desire to spoil their pets just as they would their children.

"It's not out of the norm to dress them up in bling, or carry them in a fashion carrier that matches your outfit or the outfit the dog is wearing," Cooper says. "It's a special bond, and it's more and more socially acceptable."

Which is one reason why PetSmart includes such things as a pink parka with faux-fur hoodie for dogs ($19.99) and an antler hat for cats ($4) on its list of top holiday gifts for pets this year.

Christmas spending on pets has been increasing steadily in the past decade; Vetere estimates spending this year will be up 8 percent, possibly more.

"Christmas is our busiest season, just like it is for regular retailers," says Carmina O'Connor, who with twin sister Charisa Antigua sells dog couture and jewelry in pet boutiques around the country under the name Oscar Newman. Their doggie coats, sweaters, T-shirts and dresses ($50-$150) are hand-beaded, embroidered or hand-crocheted and feature such glitter as Swarovski crystals, pearls and mother of pearl appliques.

"We've had tremendous growth — 400 percent in just our second year," she says. "Pets have become extensions of their owners, who are having children later or not at all. They want them to look good as a reflection of themselves."

Fashion designers — for people — are noticing. Isaac Mizrahi sells a line of canine haute couture at Target, after launching the collection last year at New York's Fashion Week. Ralph Lauren sells doggie polo shirts ($32), cashmere sweaters ($95) and shearling coats ($250). Like many luxury accessories designers, he also sells dog carriers: His crocodile carrier costs $18,000.

If people love to party, why wouldn't dogs? Thus, the book "Dog Parties: Entertaining Your Party Animals" by Kimberly Schlegel Whitman, wherein she advises people "who share that crazy kind of bond of pet lovers" how to throw successful parties for dogs. For Christmas, she suggests draping decorative lights on doghouses, gingerbread doghouses, dog cookies with holiday themes, Christmas stockings featuring each breed invited to the party, and, of course, "egg-dog."

And it's not all for the owners, Whitman insists. "Dogs do understand that something exciting is going on, more than we recognize," she says. "At Christmas, you're staying out, going to parties and they're getting less attention. So this is a nice time to do something special for them."

It's a long way from the days when Americans loved their pets but didn't exactly pamper them, not even at Christmas, says Vetere.

"When I was a kid, my dog Duke lived in the backyard and occasionally we'd let him in the house. Today my golden retriever Dakota has the run of the house, and he only goes outside by appointment."