Up to 30,000 D.C. public schoolchildren--more than 40 percent of the school system's enrollment--are expected to attend summer school this year in what would be the city's biggest remedial program ever.

Like last year, when nearly 25,000 students enrolled in the summer program, classes of up to 15 students will work intensively on reading and math, four hours a day for six weeks. Classes begin June 28, one week after school ends, and continue through Aug. 6.

Students who scored at the lowest level--"below basic"--in either math or reading on the Stanford 9 Achievement Tests in April will be strongly encouraged to attend summer school; if fewer than 30,000 students scored at that level, students who reached the "basic" level will be allowed to fill the remaining summer classroom spots.

The test scores were due back to school officials this week. Students are placed into one of four categories: "below basic," meaning far below grade level; "basic," or low grade level; "proficient," which means at grade level; and "advanced."

About 30,000 students scored below basic on either math or English when the exams were given last fall, but school officials said they expect several thousand will have boosted their performance to the basic level as a result of remedial Saturday classes offered at most schools since January.

Principals and teachers will use the spring Stanford 9 scores, along with classroom performance, to decide whether students in grades 1 through 5 will be promoted. For students on the borderline, a strong summer-school performance could make the difference.

In the higher grades, students will be promoted based on whether they earned passing marks during the school year. But school officials say they still will expect students to attend summer school to improve their reading and math skills if their scores on the achievement tests are low.

"The goal is proficiency for all students," said Wilma Bonner, executive director of secondary programs.

The policy is much more flexible than that of the Chicago public schools, which pioneered the concept of massive remedial summer school sessions several years ago as part of its effort to reform a failing school system.

Chicago requires third-, sixth- and eighth-graders who score poorly on the Iowa Test of Basic Skills, an exam similar to the Stanford 9, to attend summer school and retake the test. If their scores improve sufficiently, they are promoted to the next grade.

About 25,000 Chicago students in those grades will attend summer school in hopes of being promoted this year--a lower number than in the past because test scores have gone up. More than 100,000 other students in the 430,000-student system will attend separate summer school sessions, including about 5,000 fourth- and seventh-graders who were forced to repeat a grade earlier and now hope to earn the right to rejoin their original classmates.

Although D.C. officials have cited the Chicago program in setting up their summer school, they have also emphasized that teachers and principals--who should be most familiar with a student's academic performance--will decide who goes on to the next grade, rather than test scores alone.

"The local school, the principal and teachers have got to put together that whole package and see what that student looks like," said Mary Gill, director of elementary programs. The Stanford test "is one indicator--a very strong one, because tests aren't going away. We expect our students to be able to demonstrate knowledge."

Ninth- and 12th-graders who need extra course credit to graduate junior high or high schools can earn it in special summer sessions at Eastern High School or at Ballou High School.

Nearly all 146 D.C. schools will have their own summer-school program, Bonner said. Because extensive building repairs will be underway, Woodson High School's program will be relocated to Spingarn High School; Dunbar High School's program will be at M.M. Washington High School; Brookland Elementary School's program will be at Bunker Hill Elementary; Scott Montgomery Elementary School's program will be at Seaton Elementary; and Oyster Elementary School's program will be at Eaton Elementary School.

Students from Stevens Elementary, a downtown school that enrolls youngsters from across the city, will attend summer programs at their neighborhood schools or at Ross Elementary.

In addition, schools with fewer than 60 youngsters who need to attend summer school will merge their programs with other schools. They are: Hearst, Janney and Lafayette elementaries, which will send their children to Murch Elementary; Key Elementary, whose students will attend Hyde Elementary; and Stoddert Elementary, whose students will go to Horace Mann Elementary.