ONE SMALL ITEM in the "urgent" supplemental appropriation bills vetoed by President Reagan would have partially restored cuts in the youth summer jobs program. The president was right to resist the $3 billion bail-out for the housing industry that was riding on the bill, but the modest increase in summer jobs could have helped relieve the smoldering problem of record levels of youth unemployment in many cities this summer.

The summer jobs program was originally sanctified as one of President Reagan's "safety net" programs that was not to be tampered with. Even so, it lost about 50,000 jobs last year and is due to lose 140,000 more this summer. That leaves the total at about three-quarters of its 1980 level. The president's budget for next year would eliminate the program altogether--although localities could divert money from training programs to pay for it. The supplemental bill passed by the Senate would restore about 63,000 jobs--not enough, but better than no help at all.

With unemployment at the highest level since the end of the Depression, this is a tough time for workers of all ages. But the situation of low-income youths--especially blacks--is disastrous. Last month, one out of two black teen-agers seeking work couldn't find it. That was before summer vacation swelled the ranks of job seekers.

It would be nice if the private sector could fill the gap. But even when times were better, recent estimates suggest that four out of five youths who were eligible for the summer jobs program, but for whom there were no jobs, couldn't find even short-term jobs in the private sector. With the economy now providing well over a million fewer jobs for teenagers than it did in 1979, the need for government help is greater than ever.

The effort to improve the quality of summer job programs needs to be continued. Any additional jobs should be targeted on areas where youth unemployment is especially high. But as Congress considers its next moves on the supplemental appropriation, it should remember that, even unimproved, the program is a good investment.