More black and Hispanic Americans are graduating from high schools than did a decade ago, but a smaller proportion are going to college, according to two reports.

The findings suggest that many blacks and Hispanics may be skipping college because student financial aid has not risen as fast as college costs.

"Their college-entrance rate is declining," said Mary Margaret Walker of the American Association of State Colleges and Universities (AASCU), which sponsored one of the reports. "The major factors in that decline are economic."

The reports add fuel to the debate over the Reagan administration's proposed cuts in the guaranteed student-loan program and its proposed tough eligibility and income standards for all student financial aid.

"I think the terrific kind of cultural pressure for desegregation and civil rights was in the 1960s and '70s," said John B. Lee, vice president of the human resources division of Applied Systems Institute Inc., which prepared the AASCU report. "A lot of black kids went to college on that crest. A lot of that emphasis on minority recruiting by schools has declined -- it's still there, but it's not as intense."

More blacks and Hispanics are on college campuses in the 1980s than in the 1970s, but blacks in college represent a smaller percentage of those eligible for college, down 11 percent between 1975 and 1981, according to the AASCU report.

While the number of Hispanic high school graduates increased 38 percent between 1975 and 1981, the percentage of that group that attended college dropped 18 percent, the AASCU report found.

But more recently, 1983 figures show Hispanics' college enrollment improving and blacks' college participation continuing its slide, relative to both groups' pool of eligible high school graduates.

A similar study by The College Board research group -- focusing on education among blacks -- generally confirms the trend found in the AASCU study. Fewer blacks are dropping out of high school, but that has not translated into increased black enrollment in U.S. colleges.

"After 1975, the number of blacks enrolled in college stayed about the same, even though the number of blacks eligible for college increased," said Linda Darling-Hammond, senior social scientist at the Rand Corp., which prepared The College Board's report. "It may be, in part, because college costs have gone up."

Educators and researchers have offered several explanations, ranging from the failure of federal student aid to keep pace with the spiraling costs of higher education to a shift among college-eligible blacks away from traditional universities toward vocational training.

Many job-training schools have only recently become eligible to receive students using federal financial aid, perhaps partly explaining the shift.

Also, high unemployment in many areas of the country -- even among college graduates -- may have made some minority high school graduates question the value of a college degree, some educators say, particularly with the trade and vocational schools offering a cheaper, shorter and surer route to a job.

But in support of the financial explanation, the AASCU figures show that while student financial aid for college has increased, college costs have increased even more. Black and Hispanic students are more likely to depend on financial aid, since both reports show that they more typically come from low-income families.

A third report, by the National Student Aid Coalition, suggests a different reason. "Up-to-date and complete information on student aid programs does not reach into inner-cities and other communities with heavy concentrations of disadvantaged and minority students," the report concluded. "Colleges and universities do not recruit heavily in these areas, and information guides, if they are available, are likely to be out-of-date."

This group, in a report released in January, suggests that one problem is that student-aid information is not made available to inner-city students at the time when they must decide whether to take college preparatory courses.

The share of federal financial aid going to white students increased by 8 percent between 1978 and 1983, while for blacks the share decreased by almost 5 percent, according to the AASCU study.

Walker of AASCU said that, coupled with rising college costs, "The student aid dollars buy less. And there is a shift, with white students now getting more of that aid."