AS THE COUNTRY embarks on the intricate job of raising the quality of its schools, there's great value in looking carefully at those schools that are already very good. They offer reassurance that the hopes for more efficient education are not unrealistic, and they provide the best kind of guidance toward ideas that work. The Department of Education published a list last week of 144 "unusually effective" secondary schools, four of them in Washington and Northern Virginia.

What's the definition of an effective school? The criteria used here put a good deal of emphasis on test results, discipline, dropout rates and numbers of graduates who go on to college. As you might expect, the number of big-city high schools on the list is conspicuously low. The selections strongly reflect the standards of demanding middle-class parents. It is possible to argue that these choices were made on grounds unfair to the inner cities. The Maryland school system refused to participate for that reason. But if equality of opportunity is the goal, don't those standards have a certain relevance? The secretary of education, Mr. Bell, invited state school superintendents to nominate schools from which several review panels made the final choices. The results are instructive.

In Washington, they chose two junior high schools: Brookland, serving a solidly middle-income neighborhood adjacent to Catholic University, and Jefferson in Southwest Washington, with a more disparate enrollment. Both schools reflect the importance of a highly capable principal, Shirley Hammond at Brookland and Vera White at Jefferson.

In Virginia one of the choices, Falls Church's George Mason Junior-Senior High, has all the traditional advantages. It is greatly cherished by a small enclave of highly stable and prosperous neighborhoods that support it well. Under those circumstances it ought to perform effectively--and it does. The other school cited here is a more interesting example --Alexandria's T. C. Williams High. Its black and white enrollments are roughly equal, with substantial Hispanic and Asian minorities of whom many are new arrivals with little English. T. C. Williams High offers vocational education that provides a student, before graduating, with an established work record and reliable connections with local employers. For youngsters going to college, there is an unusually strong math and science curriculum and instruction in five foreign languages, including German and Russian. As an example of a school successfully serving a highly diverse city, T. C. Williams especially deserves the attention that it is now receiving.