JIMMY CARTER is paid $200,000 a year to be president. A U.S. senator's salary is about $57,000. After nine years, a D.C. policeman earns about $20,000. A Metro train driver earns about $19,500 after three years. In Loudoun County, a third-year teacher earns $10,600 and says she must "moonlight" at a second job to support herself. Is the teacher asking for too much money or is $10,000 no longer a fair salary?

By Census Bureau standards, it would appear that the Loudoun County teacher has no reason to complain. Her $10,600 income is higher than the average pay of most employed Amercians, if you include part-timers, youngsters with summer jobs and so forth. But her salary is somewhat lower than the national average for adults working full-time. And it does cost about $1,100 more per year to live in Washington, one of the five most expensive cities in the nation, than in other U.S. cities. Some of this cost may be offset by the fact that half the families in this area earn over $23,000. But for the other half, the cost of living in Washington is a special burden.

Ultimately, "enough" is relative. With $10,000, a person may be able to afford a small Washington apartment that is under rent control, drives a used car and still have money for the movies. But $10,000 is not enough to buy a house or a new car or to eat out once a week. The statistics suggest that "enough" for a local family of four is about $16,000. For an individual, it is about $10,000. But "enough" merely keeps hunger and desperation from the door. For a family of four living on $16,000 in the Washington area, everything but bare necessities becomes a luxury.

In the Loudoun case, a teacher working a second job may be tired and unable to give as much to her students. This makes her moonlighting a concern to the parents of her students. Moreover, since teachers earn more money in neighboring school systems, Loudoun County may be losing good teachers to other systems. Average teacher pay is $20,000 in Arlington, $17,000 in Falls Church, Fairfax and Alexandria -- and $11,000 in Loudoun. Loudoun has long advertised itself as having a lower tax rate than the closer-in jurisdictions. But development brings a need for more public services. The attractive low tax rate may no longer be possible if parents want good teachers.

The Loudoun school superintendent has recommended a 15.6 percent pay increase for county teachers. The school board should approve it.