THE ideal guest room probably does not have a guest in it. It is thus the ideal place to store: books that nobody wants but cannot bear to throw out, spouses who snore and knickknacks of tremendous sentimental but absolutely no aesthetic value.

If you do not put a guest in your guest room, you also need not put in it the standard essentials: extra blankets and pillows, current magazines, a reading light, towels in a range of sizes never used by people in their own homes, padded hangers, mirrors, empty drawer space, wastebaskets, a key to the house and a clock; or the considerate extras: writing paper and stamps, flowers, ice water, sewing kits and fresh miniature toiletries.

Surprisingly, it is easier to stock your guest room with all these things than it is to keep it empty. Even people who are scrupulous about never issuing invitations to anyone not within easy commuting distance have relatives or friends who take vacations in their cities, need shelter from domestic quarrels or painters, dispatch their own friends and children on vicarious visits, or misinterpret such ordinary pleasantries as "Let us know if you're in town."

Miss Manners does not deny that there are times when it is a pleasure to have houseguests, and people who are delightful to see around the clock. There is a question, however, of control. Hosts who abdicate control at the beginning are likely to lose it at a time when the other members of the family have to keep saying, "Shhh, they'll hear you."

The first rule is: Never issue an invitation that you do not want to issue.

Miss Manners has often remarked with surprise on the inability of most people to decline what they do not want. Second helpings, caresses and assignments to bake 200 cookies by tomorrow are constantly being accepted because people do not know how to refuse them.

The way to refuse a houseguest who proposes himself by saying, for example, "I thought I'd come down for a week or two," or "Can I stay with you until my furniture comes?" is to reply, "Oh, let me make a hotel reservation for you, and be sure and keep an evening open for dinner," or "Oh, dear, that's a bad time for us."

One does not say, "I'll probably be out of town then" ("Okay, fine, I'll house-sit for you") or "I'm expecting my in-laws at about that time" ("Love to see them--and I can just plop down on the couch").

The second rule, for those who have violated the first, or for those issuing any invitation, however genuinely and warmly, is: Never propose an open-ended visit.

"Come on Friday and stay through Sunday" is better than "Come for the weekend," because people tend to interpret "weekend" as they wish their employers did. It can be "We'd love to have you spend the summer--say, the Fourth of July until Labor Day," if you must, as long as the departure date is stated.

Third rule is: Yes, you may throw people out who ignore the departure date. The polite method is, "We've had such a marvelous time having you. I'm afraid we're going to need the room by Tuesday."

Then the guest room may be put to its most enjoyable use, as sprawling space for a family happily spreading out again after even the most beloved of guests has gone.