In a serious blow to the D.C. public school system's attempts at early rescue of its slowest and most disadvantaged learners, half of the 21,622 students in grades 1 through 3 failed last year to master skills sufficient to meet the school system's new standards and will not be promoted next month.

As an extension of its back-to-basics curriculum, the school system last fall launched a program called the "pupil progress plan" that required students to acquire certain math and reading skills and instituted midyear tests and promotions to ensure that progress was being made in those areas throughout the school year.

Citywide statistics released yesterday show that 6,340 students in grades 1 through 3 failed to master the required skills in reading and math and that an additional 4,306 fell short in one of the two areas. Only 9,379 students passed math and reading. Statistics for seven schools with more than 1,500 students were not available for release.

The most frequent problems among students who failed this year occurred in reading comprehension, according to Acting Associate Superintendent Vandy Jamison. No breakdown of the pass-fail statistics by grade was immediately available.

In most schools, the failing students will receive extra help from the classroom teacher and from math and reading specialists. In some other schools, special classes might be created.

Patricia Morris, president of the D.C. Congress of Parent-Teacher Associations, let out a whistle and exclaimed, "How many -- 10,000! That's mind-boggling," when told of the statistics. "I have been saying that they need to sit down and go over this plan."

Acting School Superintendent James T. Guines, however, said he was not surprised by the results since it is the first time the system has given teachers a specific checklist of skills their students must master by the end of the year and the first time in more than 15 years that students are being promoted at the half-year mark.

"These results are very understandable. This isn't Arlington, where you have a school system reflective of a higher income level. We have a school system that is 60 percent poor. . . . . In a population like that, you would expect to find the results we found."

"It doesn't say anything about the teachers we have. It's just that in Washington, we have a double job to do," Guines said.

No decision to change or possibly lower the current standards is expected until the end of the school year, Guines said. However, some school officials said yesterday that the problem may not be that standards are too high.

"There is a fairly obvious pattern emerging that the middle-class kids are doing well and the kids in the schools in the low-income communities are not. We have to try to get some additional resources to help the kids in those schools," said school board member Frank Smith (Ward 1).

Guines said he has directed the principals of every school to devise plans to give additional help in the upcoming semester to students who failed or passed only one subject area.

Guines attributed the failures in part to the socio-economic background of the students, but other school officials offered various reasons for the results.

"We started this new program in grades 1 through 3. But some of those skills that we expect students to know in grade 3, those children may not have been exposed to in grades 1 and 2," said Jamison, who is in charge of schools in the Anacostia region.

"I do not believe that children can't learn because they are socially and economically deprived," he said, noting that at Green Elementary, in one of the poorest neighborhoods of Anacostia, children have been scoring above national norms on standardized tests. "Good teaching produces good learning," he said.

"I think we're seriously going to have to take a look at our teaching personnel, either give help to the people who are not doing their job well so they will do better, or if that fails, get rid of them," said one highly placed school official who asked not to be named.

Parents had varied reactions to the citywide statistics.

Vernell Sheldon, parent of a second-grader at Bruce Monroe Elementary in the Columbia Heights section of Northwest, said she is not upset that her daughter has not mastered enough skills to go from grade 2A to 2B.

"I believe our children should be able to read. From what I've read, there are college students who can't read," she said.

Anita Wesley, another Bruce Monroe parent whose child is passing in the second grade, said, "For some of the students, the plan is all right. But for those who are slow, it's not too good of an idea."

The plan calls for parents to go over their children's school assignments at home, and teachers all year have been sending home mimeographed lessons for the parents and their children to work on together.

But Morris, of the D.C. Congress, said school officials did a poor job of explaining the pupil progress plan to parents.