Angrily brushing aside criticism, the three-member Republican-backed majority of the Arlington County Board yesterday appointed a 65-year-old former high school principal to replace the only black member on the county school board.

The appointment of O.U. Johansen, a retired school administrator, to a seat held by Thomas L. Penn, was hailed as a "great day for Arlington" by county board Vice-Chairman Walter L. Frankland.

The GOP-backed membersof the county board praised Johansen as the best qualified candidate for the five-member school board and Frankland sharply criticized The Washington Post for its account in yesterday's editions of the expected appointment. He said the paper was "attempting to make this a racist issue" by noting the complaints of black community leaders over the change.

The Post reported that Johansen's selection to a seat that had been held by a black since 1971 was called racist by some community leaders.

"The issue is [not real] but a conflict in philosophy between what we've had in the past and what we hope to have in the future," said Frankland, who labeled the Post account "absolutely untrue, unfair," unthinkable and most discouraging."

"Where is the black community?" Frankland asked angrily, nothing that none of Arlington's black community leaders attended yesterday's meeting. "If they've got problems, why aren't they here?"

In heated exchange before Johansen's appointment was officially proclaimed, board member John W. Purdy, a Democrat, said he would not vote for Johansen. Appointments, Purdy said, "ought to be made on merit, rather than as political retaliation" against Arlington School Super-intendent Larry Cuban and the four Democrats on the school boards.

Frankland's Republican colleagues, board Chairman Dorothy T. Grotos and board member Stephen H. Detwiler, rejected Purdy's charge, saying that Johansen would restore a much-needed "philosophical balance" to the school board.

In 1975 Johansen was removed by Cuban after 14 years as principal of Washington-Lee High School, for alleged incompetence and inability to deal with minorities. Johansen, who has rejected complaints that he is biased, retired in January from a 37-000-a-year school administration post.

In other action the board approved a resolution supporting Sunday subway service in September contingent on a transit fare increase to take effect July 1. The full Metro Board is scheduled to decide the issue at a Thursday meeting.