The number of students who achieve high scores on college entrance examinations has fallen drastically since the early 1970s, signaling a severe academic decline among the top group of American high school students.

From 1972 to 1980, the number of students scoring better than 650 on the verbal part of the Scholastic Aptitude Test dropped by more than 24,000 -- from 53,794 to 29,019 a 46 percent decline.

On the mathematics part of the test the decline was less steep -- 22 percent, or a drop from 93,868 students scoring over 650 in 1972 to 73,386 last year. The total number of students taking the exams remained almost steady at about 1 million.

SAT scores range from 200 to 800 points, with scores of 650 or better considered very good but getting increasingly rare. The proportion doing that well on the verbal part of the test dropped from 5 percent of high school seniors tested in 1972 to 3 percent last year; in math the proportion dropped from 9 percent to 7 percent over the same period.

Officials of the Educational Testing Service, which prepares the 2 1/2-hour exam for the College Board, said the examination's level of difficulty has remained the same over the years.

Educators suggested a wide range of possible causes for the sharp decline. Some reasons cited are that students are taking fewer difficult courses in high schools, college admissions standards and course requirements have fallen, and young people are reading less because of television and changing social values.

"It's hard to know definitely why this is happening," said Rex Jackson, assistant vice president for development at Educational Testing Service. "But there are simply fewer students now scoring at very high levels and that means there's a real decline in developed abilities. That makes it difficult for many colleges to admit and enroll student bodies that are as able as they were before . There are just fewer now in the top group."

"There's been a diminution of rigor in the schools since the mid-1960s," said Richard Berendzen, president of American University, "and this seems to be one of the results. . . People don't like to talk about it too much. But there is a very small number of people, probably just 1 or 2 percent, who have the ability to make really extraordinary contributions and we seem not to be developing this pool of talent as well as we did in the past."

The decline at the top of the College Board exams is part of a more general decline in test score averages that began on the SATs in 1964 and in nationwide high school achievement tests at about the same time. Until 1970, however, the number of students scoring over 650 on the SATs increased or femained steady from year to year, indicating that the drop in average scores was caused by an influx of low-scoring students as college enrollments surged.

During the 1970s a change set in as the SAT decline occurred across the board, among high scorers and low scorers as well. Even though the drop slowed considerably during the second half of the decade, Jackson said, the size of the high-scoring group has continued to go down. Indeed, from 1979 to 1980 the number of students getting the very highest SAT scores -- over 750 -- fell steeply, from 2,650 to 1,892 in verbal and from 9,059 to 7,675 in math.

Statewide SAT reports show a decline in the number of high-scoring students on the verbal part of the exam in both Virginia and Maryland during the 1970s. The decline in those scoring over 650 was 10 percent in Virginia and 19 percent in Maryland, much less severe than the national decline. On the math exam the number scoring over 650 held steady in the two states. However, since the number taking the SAT increased in both states, the high scorers accounted for a shrinking proportion of those tested.

No long-term comparisons can be made for the District of Columbia because detailed SAT data on the District is not available for the early 1970s. Reports on last spring's high school graduates show that the proportion of high scorers for all D.C. schools, public and private combined, was about the same as the nationwide averages. Private schools in the District of Columbia produced 89 percent of all students scoring over 650 in the city even though they accounted for just 24 percent of the city's high school graduates.

The verbal part of the SAT measures reading comprehension, understanding of word relationships, and vocabulary. The mathematical section of the multiple-choice exam tests problem-solving abilities, using arithmetic reasoning, elementary algebra and plane geometry.

Even though the SAT exam is called an aptitude test, College Board officials stress that it is a measure of complex intellectual abilities that are developed primarily through schooling. The "aptitude" involved, they say, is the capacity to do the analyticl work -- in papers and research projects -- normally assigned in college, which usually requires a strong education in elementary and secondary school, not just native ability.

"There's no reason to suppose that there's been any rapid decline in inborn abilities," said Alexander W. Astin, a professor of higher education at the University of California in Los Angeles who has directed a national survey of college freshmen since 1966. "But it does seem that students are taking hard academic courses in secondary school and taking more peripheral courses where As and Bs are easier to get. . .

"The schools are just less demanding than they used to be and [students] are lazy up and down the ability spectrum. The gifted are as lazy as the others. They're not all driven, and when they're asked for less, they do less."

Astin noted that television and a trend toward permissiveness through-out society often have been mentioned as reasons for the decline in school standards. The drop also may stem in part, he said, from the decision of many colleges in the late 1960s to reduce entrance and course requirements in reponse to students demands for more flexibility and choice. For example, Astin said, the end of foreign language requirements in response to student demands for more flexibility and choice. For example, Astin said, the end of foreign language requirements at many colleges led to a drastic decrease in language enrollments in high schools, which was documented by a presidential commission last year.

In recent years, Astin said, the general conservative trend in American education, which often carries the label "back to basics," has led to an increase in curriculum requirements at some colleges, such as Harvard, and the use of high-level competency exams at others, including American University. But Astin added: "It's very difficult to know to what extent this has taken hold and what effect it's had so far in the high schools."

Some critics of the SAT, notably the National Education Association, have contended that scores on the test have declined because the exam itself -- by keeping an unchanging standard since World War II -- has become less relevant as school and college curriculums have changed. Jackson, of ETS, said studies conducted a part of a major examination of the test score decline in 1977 showed that the correlation between SAT scores and high school and college grades actually increased during the 1970s.

Overall, SAT average scores have fallen since 1963 from 478 to 424 on the verbal section and from 502 to 466 in math. The figures currently released by the College Board on the number of students receiving different scores are for the members of each spring's senior class, a method of reporting that the board began in 1972. Before then, trends are based on figures for all students taking the test in a given year, including relatively small numbes of high school sophomores and juniors.