Man’s best friend saved Cheryl Rubenstein’s business.

The terrorist attacks of 2001 decimated her seasonal Halloween enterprise.

Rubenstein and husband Eric ran seven stores that catered to the growing number of Americans who see Halloween as a holiday to be celebrated with the same vigorous spending as Thanksgiving or Valentine’s Day. The customers were the types who not only buy costumes for themselves but fake gravestones for their yards and pumpkin-shaped lantern lights for their doorways.

The tragedy that befell the nation that September left few people in the mood for ghoulish pretendings.

“We got really hurt by 9-11; we had seven stores open and we got crushed,” said Rubenstein, owner of Costumes Inc., of Rehoboth, Mass. “We were hundreds of thousands in debt.”

But for some reason, people didn’t mind dressing up their pets as a way to break the somber tone, she said. The couple had been selling a few pet costumes through one of their Web sites — “you couldn’t keep antlers in stock,” she said.

“We turned to this little pet site that was just piddling along and said, ‘We have to make this our business now,'” she said.

At first, it was a bride-and-groom set that sold, then Santa Paws and Santa’s helper. Now it’s Buzz Lightyear, Batman, Spider-Man and other licensed characters. The sales kept money coming in at a time when they had just adopted three children, she said, and gave them time to rebuild the business.

Pet costumes make up 10 percent of their sales.

Rubenstein’s business benefits from the convergence of two consumer trend lines _ people are spending more on Halloween each year and pet owners are shelling out more to pamper their animals.

The National Retail Federation, based in Washington, predicts that Halloween spending this year will reach an estimated $3.12 billion, up from $2.96 billion last year. (About $2 billion of that will be spent on candy, according to the National Confectioners Association, of Vienna, Va.)

A recent report issued by the American Pet Products Manufacturer Assn., noted that in 10 years, consumer spending on pets has doubled, from $17 billion in 1994 to a projected $34.3 billion for 2004. The group says people spend 60 percent more on pet products than they do on toys for their children and 33 percent more than on candy.

Pam Danziger, president of Unity Marketing, in Stevens, Pa., said 80 percent of pet owners bought “extras” for their dogs, ranging from plastic balls to $150 cashmere sweaters.

To be sure, pet clothing is a small part of Halloween spending, about 4 percent of the costume market, according to Alan Geller, executive vice president of Easter Unlimited Inc./Funworld, of Carle Place, N.Y. The company supplies costumes and other non-food Halloween items.

But, Geller said, the number of retailers selling costumes destined for Sparky’s backside grows yearly.

“They all have a selection for pets,” Geller said. “The favorite for us is Super Dog.” The costume is patterned after the design of “Krypto,” a short-lived character that Warner Bros. included in the Superman cartoon series. “It’s truthfully selling across the country.”

Shawn Underwood, a spokesman for Petco, of San Diego, agreed that the sales continue to grow. “It’s a little bit more every year. The majority of our stores sell out of the costumes well before Halloween.”

The trend has spilled into that other October staple: the Halloween party. Chains such as Petco and independents will host pet costume parties on Oct. 30.

While dog owners are cash in the bank for pet stores that sell costumes, cat lovers are another matter.

Few felines will allow more than a studded collar on their necks. You can pretty much forget about that French maid costume.

“My cats aren’t very cooperative,” Rubenstein said.