Sooner or later, somebody was bound to think of it. In a town like Washington, where people want it all and expect that they can pay someone to do almost anything, it shouldn't come as too much of a surprise that there are people making a healthy living "sitting" other people's pets.

We're not talking here about the neighbor who comes in to feed the cat while you're away for the weekend or the kid down the block you pay a dollar to walk the dog while you've got the flu. These are real businesses, some complete with offices, whose primary mission is to feed, exercise and clean up after pets whose owners are otherwise engaged.

Although it might be difficult in some quarters to take pet sitting seriously, some clients swear by them. And more than one parent seeking good child care might envy the assiduous detail of logs that inform owners of their pets' activities during their absence.

"This is really an idea whose time has come," says Helen Foster, a former environmental engineer who founded the Arlington-based Pets n' Plants two years ago when she had difficulty finding someone to care for her two cats. Today, she has 22 caretakers to serve her more than 500 clients.

"Washington has so many Yuppies who live a very fast life style, yet people are putting off marriage and having families, so they have pets instead. For many of these people, putting their pets in a cage in a traditional boarding kennel would be like putting your children in a cage."

Pet sitters "are cheap at any price," says Gaile Andersen, a District resident with two dogs who uses the Arlington service. "I'd do anything to avoid putting my dogs in a kennel. This way, they get to stay home and their routine isn't interrupted."

And while pet sitters decline to divulge how much their businesses make, all assert they are doing well. "My accountant is very proud of me," says Deborah Hollander, a former hotel restaurant manager whose D.C.-based service Sit-a-Pet serves more than 1,000 clients in the Washington area.

Although there are minor differences between services, most operate in a similar manner. An initial interview is conducted, usually at the client's home, during which the service is briefed on the pet's feeding, exercise and medication needs, as well as its medical history.

Also included in the interview is information about any security systems in the house, plant needs and potential hazards. The owner turns over his or her key, takes off on vacation or a business trip, and the service does the rest. A caretaker comes in to feed, exercise and clean up after the pet and often will also water plants, take in mail and newspapers, put out the trash and rotate lights or drapes to make the home look "lived in."

For those clients who may have to travel on a minute's notice or who sometimes get stuck working late at the office, most of the sitters will, for a fee, hold on to a client's key and take over care of the pet at the drop of a leash.

Not that everything always goes smoothly. One client's key was lost and her locks changed; the result was that she arrived home late from

"Washington has so many Yuppies who live a very fast life style . . . For many of these people, putting their pets in a cage in a traditional boarding kennel would be like putting your children in a cage." a New York business trip, found herself locked out and had to take a hotel room. The services acknowledge that there can be mix-ups, but try to minimize them.

Meanwhile, just about whatever you want for your pets, these folks try to provide. "We're specialists at following instructions to the letter," says Pat Hardin, owner of Critter Sitters, the area's oldest (7 years) and largest service.

Sit-A-Pet's Hollander says she has been called on to fix bacon and eggs for one cat and dog every Sunday morning, to play Dean Martin records for another dog, and to give one cat "carnival rides" by putting it in a basket and swinging it around over her head.

At a typical daily rate of $10 (usually one visit to one cat) to $20 (two visits to two pets), pet-sitting services are not cheap, yet clients don't seem to mind.

"It's expensive, but I think it's a necessary expense," says Kathy Rouch of Alexandria, who must leave her two cats alone during her frequent travels as a meeting planner for the American Bankers Association. "When I took on the cats, I also took on the whole responsibility of seeing that they are cared for."

Says Critter Sitters' Hardin, "I think most people build it into the cost of their vacations. And it's like child care. You aren't going to compromise because you only make a certain amount of money."

Hardin says her service also has salvaged homes when pipes have burst and prevented tragedies when ovens or irons have inadvertently been left on. "I don't think," she says, "you can put a price tag on that."

All the services are quick to point out that you get what you pay for. Professional pet sitters don't just walk your dog, they walk it on the identical route you do. They don't just feed your cat, they plan menus. Critter Sitters have periodic training sessions with veterinarians and other guest speakers and have access to an entire library of pet-care materials.

Pets n' Plants' caretakers bring a peacock feather to play with -- and exercise -- cats. Most of the services also leave a daily log so the owner will know exactly what Puss or Fido ate at every meal, and what happened during each walk.

"It gets pretty graphic sometimes," admits Pets n' Plants' Foster, so her caretakers are instructed to use the phrase TCB (which stands for taking care of business). For anxious owners who can't relax on the Riviera unless they know Rover is all right, the services also will arrange calls.

Both pet sitters and their clients insist that home-sitting is preferable to leaving pets in a kennel, even though the animal may be alone for 22 hours. The cost is about the same.

"I don't like to use a kennel because my dogs are used to a lot of freedom, both in the house and the yard," says Andrew Miller, an independent television producer who owns two Akitas. "I also worry about diseases that they could pick up in a kennel, especially kennel cough."

Miller, whose wife works for an airline, says that because they travel so much taking the dogs to a kennel is too time-consuming.

Leaving pets in the hands of a friend or neighbor, while certainly cheaper than hiring a pet sitter, also has its drawbacks.

"When a friend takes care of your pet, there are some things you just can't ask them to do, like change the Kitty Litter," says Sit-a-Pet's Hollander.

It also can be tough to find someone. "In Oshkosh or Syracuse you might be able to find someone to care for your pets while you're away, but in an area like ours, people are so transient they often don't have the opportunity to meet their neighbors," says Critter Sitters' Hardin.

Finally, with friends and neighbors, you sometimes can't be sure the pet is getting the care you had in mind. "With friends or family, you don't know how much of an imposition you're making, and with that imposition, you don't know how much of an effort that person will make," says Miller. "With pet sitters, you know what you'll get, because they're professionals and it's their job."

"I think these services were designed for people just like me," says Rouch, who when traveling likes to know that her cats are left in the comfort of their own home.

"I feel that they're well cared for, but I wish I could be there with them. I like my cats a lot, but I don't think I'm eccentric."