O.U. Johansen, who was named to the Arlington School Board two years ago following his controversial ouster as a high school principal, said yesterday he will resign from the board on Sept. 1.

In a letter to Arlington County Board Chairman Stephen H. Detwiler, Johansen, 67, said he had "enjoyed the opportunity to serve during the past two years, but since I no longer have any children in the Arlington schools, I think it is time for someone to take my place who has a more direct involvement in the schools."

Johansen, a past chairman of the five-member board whose term would expire in June 1983, said yesterday that "the best thing I can say now is that it's time to retire. There was no pressure on me to resign. Every other member of the school board asked me to stay on."

In January 1975, when then-school superintendent Larry Cuban announced that Johansen would be removed from Washington-Lee High School after 14 years there, Johansen's situation became a cause celebre in Arlington. Hundreds of parents, teachers and students held meetings to protest the action, and he became a rallying point for conservative discontent.

At first, school officials said Johansen's removal was necessary because Washington-Lee renovations and curriculum changes would not be completed before the principal's mandatory retirement at age 65 in 1979.

But when Johansen filed suit in U.S. District Court in Alexandria, seeking to block the transfer on the grounds of age discrimination, school officials, said the actual reasons for the transfer were Johansen's alleged, incompetence and inability to deal with minority faculty and students. Johansen subsequently dropped his suit and reached an out-of-court settlement with the school systems, allowing him to remain principal of Washington-Lee for one more year.

The County Board named Johansen to the school board in May 1979.