GETTING JOBS for the average youngster in the District, where there are not many blue-collar jobs, is hard enough. Getting jobs for mentally retarded teen-agers approaches the impossible. But in the last few months a jobs program for mentally retarded teen-agers, in one District public school, has had unprecedented success. Last year the same program found only 20 jobs for students at Grimke School. This year 183 students are in the work- study plan. The young people, aged 15 to 21, are working at such places as the National Zoo, the police boys' and girls' clubs, Georgetown University and the public library. They are paid with money from a $30,000 federal grant.

Grimke's purpose as a special school is to prepare the mentally retarded to hold jobs by the time they are 22. Students are taught how to ride the buses, get to work on time and follow a boss's orders: the basics of how to be a good employee.

The program is threatened, however: it is on the verge of running out of money. When its budget was set, vocational counselors Mae Hancock and Sandy Schwarz did not anticipate that so many work- study jobs could be found. With 183 jobs now depending on a budget that had figured on 20, funding is expected to run out in March. To keep the program going, the financially hard-pressed school system will have to provide more money.

The school's vocational counselors estimate that of the students who stay at Grimke until they are 22--that is, those who have been unable to find a permanent job until then--about 50 percent become unemployed when they leave school. The work-study program is the answer. Dina Dillard, 19, a student who cleans tables at D.C. General Hospital, says with pride: "They liked me enough so they kept me working last summer. When I'm absent one day, all the ladies ask me where I've been. I love my job." She should not have to lose it in March.