The University of Maryland Board of Regents has given final approval to a policy that raises undergraduate admissions standards at its College Park, Baltimore County and Eastern Shore campuses and to a comprehensive plan for an academic upgrading of the Baltimore County campus.

Under the policy, which goes into effect in the summer of 1980, students will be guaranteed admission to the university if they have at least a C average and are in the top 40 percent of their high school class. The current cutoff is the top 50 percent of a high school class.

Students also may gain admission to the university through a combination of high school averages and Scholastic Aptitude Test scores, with lower grade averages requiring higher SAT scores.

University President John S. Toll said the action is "but the first step in a continuing process to raise admissions standards at the university."

In the plan for the University of Maryland Baltimore County, the regents voted to transfer part of the school of business and management from College Park to Baltimore County, establish a school of journalism at UMBC and authorize several new master's and doctoral programs.

Currently underenrolled and operating at approximately 60 percent of capacity, UMBC has about 5,000 students. University officials would like to increase that number to 7,500 by 1983.