HAVING STUDENTS pay to use schoolbooks is a bad idea. But it is an even worse idea for some students to be left without books. Surprisingly, in Fairfax County, one of the richest in the nation, those are the basic choices at the moment. Accordingly, schools superintendent Linton Deck has proposed that students be charged a user fee for textbooks, ranging from $22 a year in elementary school to $30 a year in high school.

With the $2.75 million this is expected to yield, the school system would be able to order enough books for all students and absorb the increasing costs of teacher salaries and other programs. Tose students from families with low income -- about 8 percent of the student population -- would have their books paid for through a special school system program.

Is this really Fairfax County we're talking about? Why doesn't the well-to-do county just increase the size of the school budget? The answer lies in statistics showing Fairfax's registered voters to have shifted in recent years from a majority with children in the schools to a majority without schol-age children. There is more pressure in the county now for better public transportation and other county services than for an increased school budget. This leaves some parents willing to do anything, including pay a modest user fee for textbooks, to keep the schools operating at their traditional high standard -- and to keep them from paying a higher real estate tax.

The user fees for texts may be a good idea in Fairfax, considering its peculiar circumstances of wealth and changing demographics. It would not be a good idea for other school systems with larger numbers of poor students who could not afford to pay for books. And in Fairfax, special care must be taken to ensure that the few students who can't afford the fee do not go without books for want of money or feel social disgrace at asking for a waiver. It would be shameful if that was to happen anywhere, but especially in so prosperous a county as Fairfax.