ALMOST ONE out of four teen-agers wanting jobs can't find them. Young people's unemployment--for reasons not all of which should cause concern--is always much higher than that of adults. But the rate is up almost six points since President Reagan took office, and the president is said to be considering reducing the minimum wage for teen-agers as a way of encouraging employers to hire them.

Cutting miminum wages for teen-agers would surely increase their employment somewhat. Economists estimate that reducing the minimum to $2.50 an hour, as the administration is considering doing, might knock youth unemployment down a few notches. But cutting youth unemployment by two or three percentage points would look like even less of a triumph if the jobs the teen-agers got were at the expense of low-wage-earning adults who then ended up on welfare or unemployment benefits.

The administration apparently hopes to avoid that situation by restricting the lower minimum to summertime jobs. That won't do much to help the low-income school dropouts who are the teen-agers in real trouble--and who have lost most from the rollback in special youth job programs. But if the lower wage encouraged employers to add new jobs in the summer, it might relieve the perennial problem caused by the influx of students into the labor market when schools close.

There is good reason to suspect, however, that not much new job creation is likely to occur. After all, the law already allows retail and service firms, colleges and farms to pay a limited number of students below-minimum wages for full-time work in the summer and part-time work during the school year. And almost any firm can employ a student in a vocational education course at $2.50 an hour if the job is related to his course of study. Firms must get a certificate from the Labor Department, and they must promise not to replace other workers with the students, but that doesn't seem too much to ask.

These lower minimum wage provisions have been in the law for many years. Yet only 4 percent of the 720,000 firms estimated to be eligible to take advantage of them now do so. Businesses have an even stronger inducement to hire youths needing jobs. It is the Targeted Jobs Tax Credit--initiated during the Carter administration and continued by the Reagan administration--which gives employers a tax credit equal to half of the wages they pay to low-income youths. As with any tax credit, there is some paper work involved, but it's worth a good deal more than the proposed slice off the minimum wage.

If these laws have had so little effect, you might wonder whether the new proposal is likely to do much good for anyone other than the fast-food outlets and other big employers of youth--for whom it would provide a sizable windfall in saved wages. It certainly wouldn't gladden the hearts of the millions of kids who would have gotten jobs anyway and would now be working for 25 percent less.