BY THE FALL, the D.C. public schools will join other area school districts in requiring at least a "C" average from students who participate in sports and other activities. Some coaches, students and parents balk at the idea, but it would be irresponsible for the school system not to insist, by imposing some fair minimum standard, that academic performance comes first. Not very long ago, high school sports were viewed as a tool to get the college education a student might not ordinarily be able to earn or afford. A degree meant better employment opportunities. Now, one hears that a college degree might not result in a good job while the astronomical salaries of professional athletes have made the dream of sports careers even sweeter. But a C-average standard does not deny such opportunities. It merely helps keep the most realistic goal -- a good job through a good education -- alive.

In basketball, for example, some coaches and parents are already steering promising players toward the better high school teams. Too many youths feel they are destined for stardom and that studying is unimportant. That is the worst mistake these student athletes can make. Each is just one of 550,000 high school basketball players in the United States. One in 33 will become one of the 17,000, four-year college and university team players. But far fewer collegians have a chance of making the NBA. Only the big Division 1 colleges and university players really have that opportunity. That cuts the number down to 4,200 players. Few will be drafted by an NBA team. Nearly all of them will be cut from those teams. Each season, only about 45 rookies make the NBA. That status carries no assurances either. Gary Pomerantz's April 2 article on the fate of the players on the Washington area's 1976 All-Metropolitan high school team, a piece that every high school athlete ought to read, slams that point home. They were extremely talented athletes. Not one of them came close to sustaining an NBA career.

There are many skills, vocational and academic, that high school students can depend upon to provide a living in later years. Relying on high school sports, as in trying to be the one in 3,000 high school basketball players who can say he had the right to sit on the bench of an NBA team, is not one of them. Studying as hard as possible is still the smartest course to take.