American students with "poor academic track records" made major gains in reading during the 1970s, with blacks making the most progress, but "academically able teen-agers" lost ground, particularly in math and science, a national study disclosed yesterday.

The study said that "Disadvantaged youngsters and low-achieving students made considerable gains, especially in reading and especially in elementary school.

"Black low-achievers," it said, recorded the biggest gains, improving their reading and mathematical abilities and holding their own in science.

The study ascribed the gains to federally funded compensatory education programs and the "back-to-basics" movement in reading.

But it said math and science programs suffered as a result of the emphasis on compensatory education and reading and a short supply of teachers in math and science.

The study said schools did not "help high-achieving students continue to demonstrate the potential they showed in elementary school."

The drop was particularly dramatic in science scores among "white high-achievers," the study said. There was a 4.2 percent drop among 11th-graders, a 4.1 percent drop among 8th-graders and a 2.4 percent drop among 4th-graders in this category.

The federally financed study was administered by the Denver-based Educational Commission of the States, which has prepared a National Assessment of Education for the last 13 years.

The study compared reading, math and science scores among low- and high-achieving 9-year-olds, 13-year-olds and 17-year-olds during the decade. Students who scored in the top quarter of the tests were considered "high-achievers." Those in the bottom quarter were "low-achievers."

"Though low-achievers by definition do not do as well as high-achievers, the gap between them appears to be narrowing," the study said.

Both groups improved in reading at age 9; low-achievers by 5 percent and high-achievers by 1.4 percent. Low-achievers continued to show improvement at age 13, but leveled off at 17, while high-achievers showed no change after age 9.

Math and science scores of students in the bottom quarter didn't change as the pupils grew older. However, math and science skills of high-achievers at all three ages declined, dropping by 2.5 to 4.3 percent.

Black students in both categories showed more gains than did whites, though overall performance of blacks remained below that of whites. The reading and math scores of black low-achievers improved significantly, while they held their own in science. White low-achievers recorded smaller gains.

Black high-achievers gained in reading and math skills at age 9 and 13, but their math and science abilities dropped at 17. White high-achievers did not improve in any of the three subjects. They maintained the status quo in reading, but their math and science scores dropped at all three ages studied.

The study has important ramifications for educational policy makers at the local, state and federal level. In part, it demonstrates the success of compensatary federal programs, such as Right-to-Read and Title I of the Elementary and Secondary Education Act, and the back-to-basics movement.

But it also highlights important shortcomings in public schools.

"Many good things were happening in the schools during the 1970s," said Beverly L. Anderson, director of the assessment. "Low-achievers made considerable gains, especially in reading. But we must expand the horizons of our most able students."

State and federal support for science programs dwindled during the 1970s, after receiving a big push during the late 1950s, and math didn't get the emphasis reading did, she said. Teachers were also in short supply for these subjects, and many high schools relaxed math and science requirements.

A panel of educational experts who studied the results of the study recommended:

* Increased support for math and science programs.

* A revision of high school math and science requirements.

* New programs to recruit and retain math and science teachers, and a review of teacher certification polices at the elementary school level, where many teachers have had little training in math and science.

* A reexamination of the back-to-basics philosphy. "Lower order, so-called basic skills, are not necessarily the building blocks essential to acquiring higher order, cognitive skills such as problem-solving, analyzing and synthesizing," it said.