A major new research study on American college students has concluded that some of the most significant changes in higher education over the past two decades have contributed to a "deterioration" of educational programs rather than to their improvement.

The study by professor Alexander W. Astin of the University of California. Los Angeles, says students show more positive effects -- in getting degrees, carrying out career plans, and developing new attitudes -- at private colleges that at public ones, at small colleges rather than large ones. and at colleges that are for men or women only rather than at coed schools.

Yet, since the mid-1950s, Astin notes, most of the growth in college enrollment has been in public institutions, big college campuses have became much bigger, and the number of single-sex schools has declined sharply.

In addition, Astin said, open admissions programs have brought many students with poor high school records into colleges, but few of them have succeeded. Two-year community colleges have proliferated -- with the blessing of budget-conscious legislators -- but, he said, in terms of degrees produced they have turned out to be much more expensive than other colleges because so many of their students dropout.

"Indeed, if favorable impact on students is the principal raison d'etre of American higher education," Astin said "many recent institutional and governmental policies seem to be directly contradicted by the findings of this study. . . (But) there is every sign that each of these trends is still accelerating."

Astin's study is based on a 10-year research project, called the Cooperative Institutional Research Program (CIRP), which was started in 1966 by the American Council on Education and has been conducted jointly since 1973 by the council and UCLA. It includes data from questionnaires and grade reports on over 200,000 students at about 300 colleges and universities of all kinds and sizes across the country.

Astin said it is the largest long-term study ever conducted on the effects of college education.

Among its main findings are the following:

Private colleges have a substantially greater positive impact than public ones, with students reporting that they are more satisfied with the quality of instruction and more involved in both academic work and extracurricular activities.

Small colleges rate higher than large ones in student achievement and involvement, although students at large colleges like the social life better. The large colleges do not show "economies of scale," Astin said. In fact, they actually spend more per student than small colleges because of research activity and their complex administrative structure.

Students at colleges for men-only or women-only "are much more satisfied than students at coeducational college life," Astin said. "The only area where students are less satisfied is social life. This negative effect is much stronger for men than for women."

At women's colleges, he said, women are more likely to attain positions of leadership. . . to develop high aspirations, and to persist to graduation" than women at co-ed schools.

"Apparently, women are much more likely to be verbally aggressive and to seek positions of leadership if they are not in the presence of men," Astin said. "Men seem to deter women's assertiveness during the undergraduate years."

However, he reported, women at coed colleges get higher grades, reflecting "the women's superior level of academic performance."

Among blacks and whites with similar high school grades and test scores, blacks are more likely to complete college and enroll in graduate school although they are less likely to get high college grades.

Overall, Astin said, about the same proportion of black and white college graduates enroll in postgraduate programs. However, he said, "the enrollment of blacks (in graduate schools) is substantially higher than that of whites once ability (as measured by entrance exams and grades) and other background factors are considered."

Blacks who take jobs in business or teaching directly after college earn an average of $1.000 more a year than whites of comparable background and training.

"There really is a pull now from affirmative action," Astin said in an interview. "blacks learn they have a lot of opportunities. They are sought after by graduate schools and employers."

Students living on campus in dormitories generally get far more out of college than commuters. Not only do they like it more. Astin said, but they are more likely to graduate, more likely to go on to professional schools, more likely to know professors, and more likely to become involved in extra-curricular activities.

Open admissions programs that allow all high school graduates to attend college regardless of grades and test scores have brought many students with poor academic records into colleges, but few of them have done well there.

The traditional admissions criteria --ly predict" a wide range of college performance, Astin said, indicating that colleges "have not adequately developed programs to meet the needs of less well-prepared students. . ."

Most poorly prepared students, he added, attend community colleges --"the lowest tier" of the academic system. Thus, the weakest students generally are matched "with the most limited educational opportunities."

"Clearly, American higher education is designed primarily for highly able students," Astin said. Those who are less able have many more problems, he said, even if open admissions programs give them a chance to get a college education.

Community colleges have had a poor record in educating young hihg school graduates who are aiming at careers that require a bachelor's degree, Astin said.

Although students at community colleges are supposed to be able to transfer to four-year schools, relatively few do so successfully. Of all students entering two-year colleges who say they intend to get a bachelor's degree, only 43 per cent succeed, Astin said, compared to 72 per cent who graduate from public four-year colleges, and about 80 per cent who graduate from private universities.

Community colleges "provide important services to adults, part-time students, and those pursuing technical courses," Astin said, but "for a vast number of 18 and 19-year-olds they provide the illusion of opportunity or very little more than an illusion."

Astin's study, entitled "Four Critical Years," has been published by Jossey-Bass Publishers, of San Francisco.