The regents of the University of Maryland approved a $925 million operating budget for the 1988-1989 academic year yesterday that calls for tuition increases of 9 percent for most students.

The increase, approved unanimously on a voice vote, follows an 8.1 percent tuition increase last year and brings the annual tuition at the College Park, Baltimore city and Baltimore County campuses to $1,596, a $132 increase, for state residents. A $412 rise for out-of-state students would take their tuition to $4,982. For students at the Eastern Shore campus, the 11.3 percent increase would bringing tuition to $1,540.

University President John S. Toll said the cost of a college education at Maryland is still comparable to its "peer institutions" in eight other states. Toll acknowledged that the university's tuition in 1988-1989 will be about 2 percent higher for in-state students than at Maryland's other public four-year colleges and universities.

Toll said that financial aid has been increased in proportion to the tuition increase "to try to provide an opportunity for every student to get an education through a combination of work, grants, loans and family support."

The increase continues the trend of tuition increases that have occurred at Maryland every academic year since 1979. Toll said the increase this year exceeds inflation because the university is "doing different things."

"The cost of education goes up more rapidly than inflation," he said. "Subjects become more complex. Equipment we're using becomes more complex. We have to improve to stay modern."

Toll said the increase is unrelated to a 20 percent, five-year reduction in student enrollment the regents approved in February to raise the quality of education by lowering class sizes at the main College Park campus.

The university's budget contains $5 million in state aid to compensate for the loss of tuition and fees in the first year of the lower enrollment. In the fifth year, Toll said, the university will need $12 million.

More than 66,500 students enrolled this fall at the university's five campuses, including 38,000 at College Park.

At the regents meeting and at a finance committee meeting that preceded it, only the two student representatives questioned the increase, but both voted to support it. "A lot of students are having trouble right now meeting tuition bills," said regent John J. Mattras Jr., a third-year law student.

Comparisons for the current academic year showed Maryland tuition and fees 1.1 percent lower for in-state and 1.4 percent lower for out-of-state students than seven other state institutions, from California to Texas.

Tuition at Maryland's private schools averaged $7,000 last year. Nationally, tuition at private four-year colleges has gone up about 9.5 percent a year over the last 10 years.

Tuition and fees are the university's largest source of income. In addition, the proposed budget includes a request for $381 million from the state, a 10.4 percent increase over what it sought last year. The overall proposed budget is 9.1 percent more than the current one.