What would you do if your house guests:

Brought fast foods into your kitchen rather than eat your cooking?

Left your bath looking like the aftermath of a tornado?

Expected you to pay their way to concerts and movies?

Borrowed your car and didn't return in time for you to get to the dentist?

Used your home as a free hotel?

If you fall apart over even the thought of such things, you've probably been bruised by less-than-perfect house guests. You may even have locked doors, drawn draperies and pretended to be out.

But with the economy ever-tightening, out-of-town friends and relatives are apt to spend some of their summer vacation at YOUR place.

To avoid a ride down life's fast lane between supermarket, laundry room and bank, it's best, of course, to think out the logistics of coexistence before -- if possible -- your guests arrive. Here are some things to consider from people who entertain frequently:

How long is the perfect visit ?

One to 10 days is polite as polite can be, says etiquette adviser Elizabeth Post. "The length of the visit should depend on how well you know the friends or relatives and how willing they are to adjust to your hours, your habits and the functioning of your home."

Do you really have the space ?

If not, it could be exhausting on you. Post and her husband Bill have a two-bedroom vacation house in the Florida Keys. When more than two want to visit, she says she recommends a good hotel nearby without feeling the least bit guilty, and then plans time together for all of them.

What specifics need to be discussed immediately ?

Whether arrangements are made by letter or phone, be sure to agree as to what the deal is, says gift catalog czar Roger Horchow of Dallas. With his wife, Carolyn, he spends so much time entertaining guests both in Texas and at a summer place on Nantucket, that he's writing a chapter about it in his upcoming book, Living in Style .

"Spell it out specifically," he says, "'It would be best for us if you came on this date and leave on that date, either in the morning of afternoon.' This spares hurt feelings.

"Be sure to tell guests what the activities will be, so that they will know what clothes to pack and how much money to carry. Do let them know you think it is more fun when everyone participates in the housework, if you do, and that they will be expected to pitch in -- make their own bed, take over at the stove or grill one night, pick berries, straighten the bath, or whatever else."

When guests arrive, what comes first?

Give your guests a fast tour of the house, says Washington, D.C., professional organizer Barbara Hemphill. Show them where breakfast and lunch supplies can be found in the kitchen, which racks are theirs in the bath, where extra towels and cleaning supplies can be found, which drawers and closet space may be used in the bedroom, and where the laundry facility is set up.

Ask what they would like to see and do during their visit. Let them know when you will be free to spend time with them and what activities, if any, you've already accepted on their behalf.

How much time and entertainment ?

Two evenings during the week and one day of the weekend, claims Hemphill, make you acceptably gracious. This formula is especially intended for homes in which both the husband and wife work, and there's enough going on in the community for guests to keep busy on their own.

The compleat host will ofer either a car or a bus schedule, adds Hemphill, as well as maps of the area, and guidebooks that list museums, stores, tourist sights, theaters and other sources of entertainment.

Should guests be expected to pay their own way ?

On daytime activities, yes, say these hosts. You can take turns paying for evening functions or handle it as Hemphill suggests: "'Thursday evening, we can take that river cruise or go to a play. In which way would you rather spend your money?'"

Guests, say these entertainers, should offer to treat their hosts to dinner or something else at least one evening during the visit. If it's a stay of a week or more, guests might also offer to buy some of the groceries and to prepare a meal.

What needs to be said up front about YOUR kitchen ?

"If you expect your guests to be punctual at the table for breakfast, lunch and dinner, say so," advises cookbook author and food writer Joan Nathan Gerson. "If you'd prefer that they take care of their own breakfast and lunch, eating at whatever time they choose, let them know that, too, and show them where breakfast and lunch foods are stowed away.

"If you expect them to fend for themselves in town when they can't get back in time to eat with your family, let them know this before they start out on their day.

"Ask before their arrival if their diet requires any particular foods to be on hand, so that you can avoid suffering while they stare at an empty plate at your table. Likewise, if you would prefer that they not bring particular foods into your home, spell that out, too."

And if you pop a short fuse over those who sit idly by while you slave over a hot stove, don't be timid, says Gerson, about handing them the greens to make a salad, or a towel to help dry dishes after dinner.

Gerson and her husband Allan, of Chevy Chase, have their entertaining down pat: One evening she cooks supper at home. One night they go out to a special restaurant. And finally, she will throw a dinner party in honor of her visitors including people they know or would like to meet.

Gerson believes in keeping the freezer stocked with casseroles and other items that can be served quickly after a day of sightseeing with guests. If you mark the packagers in terms of number of servings, so much the better.

Rainy days ?

Have ready alternate plans, says organizer Hemphill, including a visit to a museum, craft program or shopping outlet nearby. Of course, books, records, puzzles, games, cards can be enjoyed right in your home.

"No" to a friend or relative who wants to visit ?

"Be straightforward and honest about this," says Horchow. "It's your home. You have every right to let those people know your life is over-booked. hYou might simply say, 'While we're terribly sorry, it just wouldn't be convenient.'"

Offers psychologist Susan Shnidman, "Even though we are busy now, we sure would like to see you. Let's get together back in the city." This response is intended for those plagued at their vacation hideaway by those from the same home town. "Your genuine friends will be left with a good feeling and those out to use your retreat as a free hotel will be properly put in their place."

Adds Gerson, "Whatever the excuse, make sure your spouse is giving out the exact same story."

The impromptu arrivals ?

If it's not convenient, says Elizabeth Post, offer them a quick cup of coffee and send them on their way.

Can you ask a guest to leave early ?

Yes, if you dare to follow the lead of one graduate student whose invited guest, soon after arrival, had an emotional crisis. The student -- after a call to his mother for advice -- told his friend:

"You and I are not having a good visit. Can I drive you to the airport or train station? We can try again at another time. Let's terminate this visit rather than our friendship."