MANY PEOPLE wonder what the future will be like when the administration's budget proposals take hold some months hence. But for holders of public jobs under the Comprehensive Employment and Training Act (CETA), the future is now. All over the country, state and local governments have stopped filling vacancies among the 350,000 CETA jobs, and by the end of summer all current jobholders will be laid off. In some cities, Washington included, layoffs have already begun.

Not only jobs but also valuable services are being lost. In the District, there will be fewer playground supervisors, less parking enforcement and less help for elderly shut-ins, unemployed youths, alcohol and drug abusers and people who can't speak English. In Rochester, sidewalks won't be repaired, day care for the children of working women will be cut back and cops will be taken off the beat to do record-keeping now done by CETA workers. In rural Rio Grande communities, garbage will go uncollected and other municipal services will be curtailed.

These losses may come as a surprise to people who adhere to two widely held beliefs about CETA. One is that all CETA jobs are "make-work." The other is that CETA workers simply substitute for regular public employees who would otherwise be hired to do their jobs. Most people who profess these beliefs fall to note that they are mutually contradictory. If CETA jobs are make-work, then, we trust, local governments would not hire people to do them on their own. But if CETA workers replace regular government workers, what they do must be worthwhile.

In fact, for most CETA jobs neither of these views has been correct. CETA hired hundreds of thousands of disadvantaged people who would otherwise not have been hired to do useful work that would otherwise not have been done. Most of these people benefited from the experience so that, careful comparisons show, their subsequent earnings were substantially higher than those of people like them who didn't get helped. Thanks, moreover, to new requirements for mixing work and training, to closer coordination with private employers and to stricter eligibility limits, the usefulness of the program was increasing substantially.

CETA was an obvious first target for the administration because, unlike most social programs, it is not protected by an organized group of professional workers who stand to lose their own jobs. The people who hold CETA jobs don't organize letter-writing campaigns. The only way their loss will be detected is in higher welfare and unemployment counts, higher local taxes and fewer community services.