One of the nation's most prestigious education research groups predicted yesterday that the next 20 years should bring a "golden age" for college students as their schools work to stem enrollment declines but hard times for many colleges and their teaching staffs.

The Carnegie Council on Policy Studies in Higher Education, in its final report, projected a 5 to 15 percent overall drop in college enrollments over the next two decades. The largest decline will occur among the traditional 18-to-24-year-old student group and will cause "a fundamental, almost radical change in higher education," the council said.

"A downward drift in quality, balance, integrity, dynamism, diversity, private initiative, and research capability is not only possible, but quite likely in higher education," according to the council.

At the same time, students proposing to attend college "will be recruited more actively, admitted more readily, retained more assiduously, counseled more attentively, graded more considerately, financed more adequately, taught more conscientiously, placed in jobs more insistently, and the curriculum will be more tailored to their tastes," the group added.

In its report, entitled "Three Thousand Futures," the council said the problems facing higher education will not be uniform nationwide. The East and Midwest will lose about 10 percent of their comparative share of enrollment, resulting in the most severe difficulties. But schools in the South will grow by 5 percent, and the West and Southwest are likely to experience a 10 percent college enrollment growth, the report said.Those schools will have fewer problems, it said.

At a news conference here yesterday, Clark Kerr, chairman of the council, said his group discounted predictions of an enrollement decline of up to 50 percent.

While there will be a 23 percent drop in the 18-to-24-year-old student group, he said, that figure should be offset by several factors, including a growth of adults, women and minorities attending college. In addition, he said the college dropout rate is likely to ease from its present 40 percent level.

According to the council's findings, the percentage of women undergraduates is likely to climb from 37 percent in 1960 to 52 percent by the year 2000.

Kerr said the nation's graduate schools are in substantially better shape than undergraduate programs and will not feel the enrollment squeeze as much.

The schools least likely to feel the enrollment pinch in the future are big research institutions, top liberal arts schools and community colleges that have expanded their role to fulfill social as well as academic needs, he said.

The most vulnerable, Kerr said, will be about 600 "less selective liberal arts universities" that recruit locally and do not have flexibility to lower entrance requirements.

Yesterday's report by the council is the last in a series of more than 100 studies on education done since 1967 by the council or its predecessor, the Carnegie Commission on Higher Education. Kerr said additional education report will be done in the future by the Carnegie Foundation for the Advancement of Teaching.