Planning research Corp., a major professional services company based in Washington, reported flat earnings for the year ended June 30 although revenues rose 17 percent to a record $262 million.

President John Toups attributed the sluggish profitability to a loss from the sale of two divisions at one subsidiary as well as reserves for possible losses on substantial operations that were interrupted by the revolution in Iran.

Dart Drug Corp. reported separately that its profits increased sharply in the second quarter and six months ended July 31. President Herbert Haft attributed the improvement to tighter expense controls and good summer sales.

Planning Research profits totaled $4.97 million in the recent year compared with $4.89 million a year earlier, with per-share earnings of 72 cents in both periods. The fiscal 1979 sales volume was PRC's first excess of a quarter-billion dollars.

Adverse factors affecting PRC ,rofits included reserves of $2.9 million on potential losses in Iran ($2.5 million in the third quarter and $346,000 in the final quarter, both after tax effects). Among PRC's overseas activities, the company was engaged in design and construction management of roads, highways and bridges in Iran. PRC also was designing and supervising construction of marine terminals for the oil and gas industry in Iran.

PRC also suffered a loss of $182,000 in selling the European and North American divisions of an industrial engineering management consulting subsidiary. The losses were offset partially by a $3.2 million gain from selling Logica, a London-based computer programming firm.

The Washington firm, with 280 offices around the world serving clients in 61 nations, also announced the election of Willard Rockwell Jr. to the board of directors.

Rockwell retired last February as chairman of Rockwell International Corp. after 11 years in that position. He now is chairman of Rockwell's board executive committee.

Robert S. Holcombe was named yesterday to a new post of vice president and general counsel. Previously he was assistant general counsel and corporate secretary of Indian Head Inc. of New York.

Dart's profits for the recent quarter soared 52 percent to $1.2 million (70 cents a share) from $791,000 (43 cents) a year ago as sales increased to $59 million from $53 million. Six-month profits were $1.4 million (81 cents) compared with $956,000 (52 cents), a gain of 49 percent, as sales rose to $109 million from $100 million.

The Landover-based firm, which operates 86 drug and Crown book stores in the Washington, Baltimore and Richmond markets, completed remodeling three existing stores in the first half of the fiscal year, resulting in higher sales at those units, Haft stated.