The University of Maryland's board of regents voted yesterday to raise admissions standards and to ease restrictions on the number of out-of-state students who may attend the university.

For the first time, the rules include a list of 12 college preparatory courses that prospective students must take in high school.

The rules also raise the sliding scale of grade-point averages and aptitude test scores needed for admissions. The new rules require at least a C average in high school and a combined score of 650 out of a possible 1,600 points on the Scholastic Aptitude Test (SAT). Previously, students could be admitted to the university with the minimum SAT total of 400, provided they had a grade average of slightly above B.

The SAT requirement drew objections from Regent Clarence Mitchell, former director of the Washington office of the NAACP. Mitchell said it would "restrict the admission of black students," who average about 100 points below whites nationally on both the verbal and mathematics parts of the test.

"If it is our intent to reach out and enroll more minority students," Mitchell said, "this is the exact opposite of what we should be doing."

But the board then voted 11 to 1, without further discussion, to approve the new requirements. Following the meeting, University President John Toll said he believes that the new rules will have "no effect on our affirmative action program."

At a regents committee meeting in November, when the rules tentatively were approved, Toll had stressed that the university would allow 15 percent of each freshman class to continue to be admitted without meeting the minimum requirements. About half of the university's black students now are admitted under this exemption precedure, he said.

The higher standards at the University of Maryland, which will go into effect from 1984 to 1988, are part of a nationwide move toward selectivity in admissions at many state colleges. Toll said the increase in the number of out-of-state students permitted at Maryland, from 15 percent to 25 percent, will raise the quality of the student body.

Comptroller Louis Goldstein, an ex-officio regent, expressed concern that some Maryland residents might be turned away if more nonresidents are admitted. Toll said, however, that in the future the same admission standards would apply to both Maryland residents and out-of-staters.

Toll said the university now turns down many out-of-state applicants with better credentials than the Maryland residents it accepts. Students from out of state pay about three times more in tuition than Maryland residents, he added.