Parents who traditionally rely on teen-age baby sitters to get through the summer months had better prepare for the worst. Experts are predicting that any teen-ager can get a job this summer -- and the best can pick and choose. That means teen-age sitters probably won't come cheap.

There are some things parents can do, according to several local teen-agers, to make their offer more attractive than others.

"Basically," says Amanda Rice, 15, the ideal family to sit for has "a double phone line so you can talk and not have to worry about emergencies not getting through; they have a television and a radio; they have some kind of nice food; they have well-behaved kids; they leave good instructions so you know what to do or who to call in case of emergencies, and they pay well."

"Some families," says Lizzy O'Hara, 16, "make you feel like you can walk in and watch television comfortably, and use the telephone without feeling that you're going to be executed if they find out. I like the feeling that it's homey, that it's a job but that you're not something like a secretary, that you don't get dressed up and you don't have to talk to them as if they are a boss ... you don't have to put on a mask or an act, and the parents don't put on a mask either -- they act as they would around each other."

Stockpiling junk food is a definite plus, most teen-agers agree, because, as 15-year-old Fern Zamoff explains, "with no parents around you can kick back and enjoy yourself a little bit." And if you're asking the sitter to feed your children, don't make this an occasion for insisting that little Susie eat peas if she hates them. Leave something that's easy to prepare and that your children enjoy -- a pizza, say, or their favorite TV dinner -- so they learn to associate the sitter with having a good time.

The $2 Hour "I hate when they ask, 'How much do I owe you?'" said one young woman, reflecting the embarrassment teen-agers often feel talking about money. "Let them figure it out. Or let them ask in advance, 'How much do you charge?' " It's especially awkward when parents act shocked at how much a baby sitter is charging.

"Just asking for money is hard," confirms Elizabeth Sheinkman, agreeing with what 15-year-old Marta Ferro has to say: "If they totally underpaid, I wouldn't say anything -- but I wouldn't go back again." Thus at least two mothers never found out that the reason they kept getting turned down by their favorite sitter was that the fathers, who drove the girls home, consistently underpaid them. One father would pay for two hours, for example, when the girl was there for two hours and 10 minutes. "To gyp you for that little money -- it's not worth sitting for someone who would do that."

To keep baby-sitting affordable, parents often have to weigh trade-offs between younger and older sitters. Parents often test the waters with "responsible" 11- and 12-year-olds by asking them to sit a couple of hours on a Saturday afternoon. The advantage of the younger sitters is that they're more likely to enjoy playing with the little ones, often for $1 or $1.50 an hour (plus soda and potato chips). The kids are usually delighted with this; the house, however, is often a wreck. Although older sitters may give parents more peace of mind and are able to keep a lid on rowdiness, once they reach dating age they're sure to expect more money and are rarely available Friday or Saturday evenings.

"Some people used to pay me just a dollar an hour," says 12-year-old Brody Mullins, a male sitter in big demand on a block dense with male children. "It really isn't worth it." Much to the alarm of other parents in the neighborhood, Mullins was hired by a customer who paid $3.50 an hour, setting an awful precedent.

"It's sort of hard to ask for $3," says Marta Ferro, "but when you really think about it, it's a hard job. You have a lot of responsibility. And if the kids aren't asleep you have to really cater to them -- it's quality time."

"I've charged the same price -- $2 -- since sixth grade," says DeeDee Swesnik, who at 15 is considering a rate increase. "The people I baby-sit for now give me a tip anyway so it usually evens out as if I were charging more. I don't know if the other people could afford it. I wouldn't want them to think they have to be home at a certain time because they couldn't afford it."

"I don't charge anything -- I expect to be paid but I don't have a certain fee," says Lizzy O'Hara. "Sometimes the parents say, 'Oh isn't that cute, she doesn't charge anything,' so they give me a couple of extra dollars. One time I didn't see the kid the whole time -- the kid came in the same time the mom did, and she gave me $4 an hour. In the long run it's a better system."

"I charge between $3 and $4 an hour," says Amanda Rice, "but if someone pays me a small amount I may be perfectly happy with that. It depends on how well-behaved their kids are. If it was a lot of work I would resent it if they were really stingy. If their kids were well-behaved or asleep, I wouldn't expect as much."

Parents who expect the sitter to do extras -- cook or wash dishes -- should pay extra. Many also pay higher rates, or tip liberally, if the sitter has to stay past midnight -- or if the parents arrive home later than they said they would. And if you have to cancel, you should still pay for at least a couple of hours -- because chances are the sitter turned down other jobs to hold the time open for you. This holds true for the unpopular few parents who double-book -- reserving two different sitters so they'll be sure to end up with at least one. If you want that kind of certainty, be up front about it -- or offer a retainer to the sitter you're keeping on standby.

Teen-agers generally agree that hardship pay is appropriate for: infants (who are scary, and require -- yuck -- diaper-changing); children who are sick, whiny, spoiled, bossy, manipulative (have we left anyone out?), at a difficult stage (e.g., perpetual "no" or "why" machines), or given to crying or temper tantrums; more than two children; siblings who fight, or children of any age who resist supervision and think the goal of a parents' evening out is to see who can get the baby sitter's goat.

The ideal setup, says 12-year-old Matt Engel, is "two kids who don't try to challenge me. Most of the kids I babysit for test me -- they want to see if they can handle me. I like it when they don't scream or get too wild and see what my limits are. I don't like bossy kids."

You can usually predict which kids are likely to be obnoxious or have temper tantrums, says DeeDee Swesnik. "When the parent says a bedtime and the kid starts getting really angry and the parent changes it, you can tell. Or when the kid is whining to his or her mother."

"Sometimes it just seems like its the luck of the draw when parents have a well-behaved kid," observes Amanda Rice, "but often it seems that if the parents are either too strict or very lenient, the kids tend to be destructive."

Do's and Don'ts for Parents It helps a lot if the parents spend a fair amount of time preparing their kids for a new baby sitter and allowing time for them to get acquainted while the parents are still there. "It's terrible," says Elizabeth Sheinkman, "if the parents go out and the baby's asleep and then wakes up." Andrea Horowitz feels better if she can get to know children doing a daytime job, or playing with them while one of their parents is busy elsewhere in the house, "to sort of ease into the job."

Teen-age girls who haven't yet met the family they're sitting for sometimes feel more comfortable being picked up the first time by the mother rather than the father. And if you can't walk or drive them home, you should send them home by cab. Or if they live on your block, their parents agree that they walk home alone and you are alone at home with sleeping children -- insist that they call you the minute they get home.

Be sure there are things for your kids to do, and anticipate any problems. The worst kind of job, says Fern Zamoff, is "when I'm hired for an all-day job and the parents know the kids don't get along that well, yet still leave barely anything to do, or intend for the kids to spend the whole day interacting. That can only set things up for problems."

Every sitter interviewed agrees on the importance of leaving a full set of emergency instructions and being as explicit as possible about house rules. Can Noah have cookies at bedtime? Is it okay for the sitter to have a friend over after the children are asleep? If not, say so -- in advance.

"Tell them what the kids like and don't like," advises DeeDee Swesnik, "and what their habits are -- even if you take them for granted."

And be sensitive. Many parents think joking is the best way to talk to adolescents, but it's easy to offend teen-agers or "gross them out."

"Some people ask things they shouldn't," says Marta Ferro, offering as an example of what not to say: "Are you a good student? You look like a good student. Why aren't you out on a date?"

"A lot of times they do that," says Rennie Crocker, 16, "because they want to find out what you're like, but they shouldn't ask you personal questions that aren't related to baby-sitting."

Or as Matt Engel puts it: "I like to be treated with a little respect."

Pat McNees, whose daughter baby-sits, writes frequently about families.