At the University of Michigan's Ann Arbor campus, the stately stone mansions on Washtenaw Avenue house the fraternities and sororities of the campus' white majority. Their beer-drenched parties, the football revelry, the annual slop-fest in the mud define a college life that seems increasingly irrelevant for the school's shrinking black minority.

There are eight black fraternities and sororities at Ann Arbor, but none of them has a house, and they give few parties. Pledge classes get smaller every year. The small and declining number of blacks on Michigan's campus is insufficient to allow these clubs to thrive.

"None of the black fraternities can afford to have a house," said Phi Beta Sigma President Michael J. Walker, who runs the fraternity from his small apartment. "Our numbers are so small . . . . That's a big factor in the sense of unity blacks have -- we're kind of homeless."

Fifteen years after a student strike organized by the Black Action Movement (BAM) forced the Michigan regents to set a target of 10 percent black enrollment, that goal appears more elusive than ever. With more blacks leaving college and still fewer deciding to go in the first place, Michigan has one of its smallest black enrollments in more than a decade -- 5.1 percent of the student body.

That trend is mirrored nationwide, according to surveys and interviews with college admissions officers. The number of blacks attending college in America is going down.

The declining number of minority students is a central topic of discussion in college minority-affairs offices, in student unions, on the pages of the campus press, and among educational researchers who have produced a flood of reports on the subject recently.

Harvard psychiatrist Alvin Poussaint calls it a "crisis" for black America amounting to a fundamental redistribution of the nation's intellectual capital. A headline in Education Week called the problem a "time bomb."

Campuses nationwide reflect similar patterns:

*Of 34,000 undergraduates at the University of California at Los Angeles last year, only 330 were black -- a figure that Ralee Soporin, the undergraduate admissions director, called "absolutely devastating." The reason? According to Soporin, only 900 black high school graduates each year in California meet the admissions requirements to attend University of California schools.

*At Ohio State University, Dr. Josue Cruz, assistant vice provost for minority affairs, said black and Hispanic students are bypassing Ohio State as tuition costs have skyrocketed. While black students a few years ago could get as much as three-quarters of their tuition paid for with grants, he said, more minority students are borrowing money in greater amounts.

*At Franklin and Marshall College in Lancaster, Pa., the number of black freshmen declined by 50 percent last year, down to just 13 this year.

Nationally, black college enrollment peaked in 1976 at between 10.2 percent and 10.5 percent, after two years of dramatic growth spurred by actions such as the BAM student strikes at Ann Arbor. Black enrollment increased by 19 percent nationally between 1974 and 1976. But then the growth stopped.

In 1976 the Supreme Court ruled that Allan Bakke, who is white, could not be denied admission to a California medical school that had set aside a number of places in the class for black applicants. Most of those interviewed agreed that this court ruling, intentionally or not, may have eased some of the intense pressure on colleges to desegregate. In any case, starting in 1978, black enrollment began to decline.

A report this year from the American Association of State Colleges and Universities (AASCU) found that between 1975 and 1981, although the number of blacks graduating from high schools increased by 29 percent, the percentage of those college-eligible blacks going on to college dropped 11 percent. Another report, from the College Board, concluded that blacks' gains made in the 1970s were gradually eroding in the 1980s.

There is dispute over the actual numbers, underscoring the complexity of discussing the issue in strictly numerical terms. For example, the black enrollment rate is higher at two-year colleges than at four-year ones, and some surveys distinguish between the two. Also, the decline in black enrollment is often obscured by figures showing overall increases in minority enrollment -- although Asian students accounted for the bulk of that increase.

But there is a broad consensus from students, statisticians and educators that a problem exists. And because higher education has come to be viewed as the best avenue for any group trying to escape the cycle of poverty, the declining numbers for blacks could lead to what Poussaint called a "permanent black underclass."

"A lack of education locks us more into a dependency situation in society," Poussaint said. "For the black community, education has been the primary way we have moved up into the middle class and into professional jobs. It also increases our political effectiveness. Education is very vital to the black community economically, so I think this is a very critical item for a community that's been poor and oppressed."

"The state of black education is in a crisis right now," said Frank Matthews, a professor of legal studies at George Mason University who published a newsletter called "Black Issues in Higher Education."

The Rev. Timothy S. Healy, president of Georgetown University, recently told the American Council on Education: "Nationally, college by college and university by university, we are pushing equality of access onto the back burner. All of us acknowledge the ideal of integration, but our zeal for keeping access open, and for working at the integration of faculties, has slipped. In some institutions, it has disappeared."

Those who have studied the decline of black college enrollment attribute it to a variety of social and economic factors. On the economic side, the costs of a college education have skyrocketed for families, black and white. But since 1981, the annual increases in federal student financial assistance has not kept pace with inflation.

The Reagan administration has consistently defended student-aid cuts by saying they primarily affected students who did not need help. By cutting those students out, the administration argues, more money is made available for truly needy students. The federal aid package has generally shifted from grants to loans during the last four years, and larger family contributions are expected to cover escalating costs.

Blacks and other minority students have traditionally relied more heavily on financial aid than have white students, according to several surveys, and they also tend to come from poorer families unable to make large contributions to college costs. The AASCU report found that since 1978, aid money to enrolling white students increased by almost 8 percent, while aid to black students decreased by 4.7 percent.

The shift from grants to loans has also discouraged some minorities, who fear being burdened with thousands of dollars of debt after graduating. "Usually, minority students are coming from underprivileged backgrounds," said Michigan law student Roberto Valdespino, who talks to prospective minority students as part of the Black and Hispanic Law Students Society. "Big, huge loans scare them. A $5,000 loan sounds like a mountain to them."

Valdespino should know. He and his wife will leave Michigan law school with a total of about $100,000 in debts accumulated during their undergraduate and law school years. Also, because of changes in the guaranteed student loan program, those debts cannot be combined into one monthly payment. "We'll have to make nine or 10 different payments -- about $500 or $600 worth of school loans each month," Valdespino said.

At Michigan, Associate Vice President Niara Sudarkasa prepared a detailed report for university regents on minority recruitment and retention, and recommended that all qualified in-state minority students be supplied with financial aid packages of $5,500 each.

She also suggested increasing the more modest "merit" awards to outstanding minority students and -- in perhaps her most controversial proposal -- urged that less emphasis be placed on traditional college entrance examinations, which some researchers have said may discriminate against nonwhite students.

"The financial aid factors were very critical in this decline," Sudarkasa said in an interview. "In Michigan, the recession in the automobile industry hit black families particularly hard. The purchasing power of black families declined almost 20 percent . . . . My conclusion is that first we have to look at the economic factors."

Many disagree with Sudarkasa's findings, although her critics divide into opposing camps. Some argue that Sudarkasa and other academics like to blame the Reagan administration in order to avoid addressing their own recruiting failures and the more complicated issue of whether minorities are made to feel at home on predominantly white campuses.

Another view, advanced by blacks and whites, is that high schools and elementary schools, and blacks themselves, are to blame for failing to prepare young blacks for college.

"It would service those students if, instead of blaming the Reagan administration, we went back and looked at what is happening in grammar schools and high schools," Clarence Thomas, chairman of the Equal Employment Opportunity Commission, said in an interview."You may not be able to go to Harvard because of budget cuts , but how much does it cost to go to UDC?" he said, referring to the University of the District of Columbia, a public institution. "Blacks went to colleges, which were predominantly black colleges, for a hundred years without a lot of government support."

A sociological survey of black college students conducted at Michigan identified four "nonformal educational factors" that determine whether blacks stay or leave: isolation, participation in campus activities, the number of minority faculty members, and the number of "nontraditional" or "non-Eurocentric" course offerings.

With many cash-strapped colleges now swinging their own budget axes, courses on subjects such as African history or black American literature are disappearing from course catalogues.

According to black students and some school administrators, the university environment has become less congenial for blacks in recent years. There has been a series of isolated incidents of racial hostility on campuses nationwide, including:

*Racial incidents at Brown University, where several black students have reported being vocally harassed by white students, and where a bottle-throwing incident resulted in a student antiracism rally and a letter to parents expressing concern over the upsurge in racially motivated attacks.

*Complaints by black students at Ohio State University and at Bowdoin College in Maine accusing the schools' newspapers of using racial slurs.

*A sit-in by black students at the University of Pennsylvania after several reported incidents of racial harassment.

"Students are seeing a more homogenized student community here," said Douglas E. Johnson, a minority counselor in the office of new student services at the University of Wisconsin-Madison. "I think the whole climate is changing, the whole atmosphere. It's more difficult for a minority student to feel comfortable here. It's not limited to the campus -- it's the whole country."