ABOUT 12 YEARS AGO my trusty, neighborhood teen-age baby sitter arrived for work with an announcement: She was raising her rates. Henceforth, she was charging, not the 50 cents an hour baby sitters had charged for as long as anyone could remember, but an unheard of 75 cents an hour.

Now this was Before Inflation, and long before wage and price controls and ceilings and guidelines and all the rest of those economic stabilizers, but I knew even then that a 50 percent increase was a little wild. "Are you going to provide some additional services, such as washing the dinner dishes after the children eat?"

She hesitated and then agreed. "You know," she said, by way of explanation, "the price of movies isn't 25 cents anymore. And," she added, "you might want to know that all the baby sitters in the neighborhood are raising their fee to 75 cents, too."

That was almost too much. The last thing a working mother needs is a teen-age baby sitters' cartel. I had already heard stories about them demanding special rates after midnight, extra money for more than five children or for babies in diapers or houses without television. And for all the Cokes and potato chips parents socked away just to keep baby sitters happy, some of them didn't even show up on time for work and when they did, they sat around on the phone with their boyfriends instead of reading to the kids. Seventy-five cents an hour for that?

But of course I paid. This baby sitter did show up on time and she did read to the children and she didn't entertain her boyfriends or throw wild parties. For baby sitters like that, you pay.

Well, a footnote to the economic upheaval of the '70s is that the standard fee for baby sitters went from 75 cents an hour to $1 an hour and most recently to $1.25. But that, in an age in which it costs $4 to get into a movie, is not exactly a teenage fortune, a point Libby Horne, 15, attempted to make diplomatically in a recent issue of the Hollin Hills Bulletin.

"The average sitter in this [Fairfax County] community makes $1.25 an hour," she wrote. "Why is the pay so low? Because watching kids is the easiest thing in the world. Just tuck them in bed and turn on the TV -- no hard labor involved at all, right?

"Wrong. Employers fail to realize how much work is really involved in baby-sitting. During a regular job, children must be fed, washed up, put in their pajamas and put in bed, and cared for should they become violently ill. With younger children, diapers must be changed, bottles prepared and babies held, burped and rocked to sleep. Sometimes dinners must be fixed and dishes cleaned. . . A baby sitter is responsible for breaking up arguments, playing with children, cleaning up their messes, making sure furniture is not broken or harmed, and nursing any wounds."

Libby Horne followed her discussion with a six-point proposal for baby sitters that included such revolutionary ideas as charging $2 an hour for two kids, plus 50 cents more for each additional child, and a dollar more per hour after midnight. She also suggested that baby sitters stay off the phone and be prepared to protect the employer's property as well as his children. The idea, wrote Horne, is to "benefit the employers and the employes by upgrading baby-sitting to a more professional level."

But that's not exactly the way Libby Horne's customers saw it, "I had a regular baby-sitting job with one family," she said, "and after the lady read the article, she called me and said she wouldn't be needing me anymore. She said she didn't want anyone who charged that much.

"At first, most of my friends were going to charge $2 an hour. But when they found out that some people we sit for around here wouldn't pay that much, they went back to their old rate. . . It's kind of left me in a bad situation, I don't get as many calls as I used to."

Libby Horne arrived at her $2-an-hour figure by using the traditional benchmarks of teen-age economics: the minimum wage and the cost of a movie. And she also compared lawn-mowing fees to baby-sitting fees and saw the difference. "Mowing a lawn for three hours, you'd probably get $10. Baby-sitting, you'd probably get $4."

There is nothing easy about sitting here typing away at a column whose logical conclusion is that we should probably be paying baby sitters more than $1.25 an hour these days, or that neighborhood baby sitters ought to band together and set uniform standards for performance and pay. With two little children, this is a column that could cost.

But in fact, this is what teen-age boys have been doing for years, simply by agreeing informally that the Joneses have a $10 lawn and the Smiths have an $8 lawn, and you don't hear too many stories about boys undercutting each other for lawn-mowing jobs.

It seems that the old story of women's work being worth less than men's work starts when people are very young. But baby sitters also have an image problem in that their employers' perception of their work is that they sit around and watch children watch TV. That kind of baby-sitting obviously is easier than pushing a lawn mower. Libby Horne is trying to make the point that a good baby sitter does work and that taking care of children is something that should be valued.

Maybe almost as much as taking care of the lawn.