WITH ALL THE "Eurekas!" accompanying the "competency-based" curriculum D.C. school officals with institute in 26 schools next month, you'd think they'd discovered some magical program to help students read, understand and write better. Actually, the program and the thinking behind it are more on the order of, say, reinventing the wheel.

Think about it.A curriculum that offers a well-defined series of objectives for students and a quick way of determining whether students are reaching those objectives - i.e., whether they're learning their subjects. That sounds to us suspiciously like the old system of lessons and homework for most of the week followed by a test on Friday. There was a time when students expected a test every week and knew it would cover material from the week's lessons, so they tried to make sure they knew their stuff. And, at bottom, the D.C. schools' "new" curriculum seems to us to represent exactly that. To which, incidentally, we say: Think God. We think the revised program is a credit to School Superintendent Vincent Reed and the school board.

For at least a decade Washington's school system has been inundated with "innovative" programs, many of them poorly thought out, supervised and monitored, that were supposed to improve students' ability to read and do math. Instead, students' average achievement scores fell during the decade to low levels and stayed there. There were numerous causes for this decline, but we think behind it all was an attitude, at the top of the school system, of valuing innovation for innovation's sake and of believing in miracle cures for the serious problems Washington and other urban school systems must resolve. Fortunately, Mr. Reed and the school board have a more discriminating attitude toward educational innovation and the willingness to face squarely the tough problem of improving student performance.

Encouraging, too, is the enthusiasm the program apparently has generated among school personnel. The Washington Teachers Union has endorsed it, and teachers were involved directly in its planning. More than 100 school principals responded when Mr. Reed sought the 26 schools willing to volunteer for the curriculum's preliminary tryout. Mr. Reed himself has cautioned against expecting quick, dramatic improvements. But at least - and at last - the District's schools seem to be getting back into gear.