STARTING THIS fall, high school diplomas awarded by the District school system should begin to mean more. Requirements for graduation will be stiffened as part of an effort to end the lamentable tradition of "social promotions" in which little more than time-in-grade has been needed to receive a degree.

Under the new requirements, students will have to take additional courses and pass standardized competency tests before receiving diplomas. Those taking business courses, for example, will be tested in such subjects as business math, English and shorthand. College-preparatory students will be checked out in literature, history and math. Also, the D.C. system will become the first in the metropolitan area to require that all students take one year of a foreign language.

To some, one year of foreign language may seem a trifle, and not worth the time. But Superintendent Vincent E. Reed, a vigorous advocate of a tougher curriculum with a back-to-basics emphasis, sees it as an important complement to the four-year English requirement. The study of other languages can assist students in the use of English as well.Depending on when they begin and the level of their skills, students in the District system may move up through fourth to fifth-year levels of instruction.

The changes mean that the city's minimum high school standards will include four years of English, two years each of mathematics and science, one year of U.S. history, one year of foreign language and a half-year of District of Columbia history.

There is no magic in merely loading up or rejiggering the curriculum. How well subjects are taught and how effectively students are challenged are just as important. Those teachers who survive the reductions of staff caused by budget cuts and shrinking enrollments will be under pressure to bring students up to the necessary -- and tested -- competency levels before promoting them up and out. Good teachers should be eager to make these changes work.

Students, too, should welcome the difference. In the past, too many "graduates" have been the victims of an academic hoax, learning that their diplomas exaggerate their mastery of skills and their ability to function in the world of work or in the halls of higher education. The latest changes are what students of this city deserve for a fair crack at adulthood.