Dart Drug Corp., a Landover-based retail drug and book company, reported yesterday that profits more than tripled in the six months ended July 31.

Planning Research Corp. and Flow General Inc., meanwhile, posted record gains in the fiscal year ended June 30.

According to Dart President Herbert Haft, earnings surged in the recent quarter because of a significant increase in sales. Net income for the second quarter alone was $791,000 (43 cents a share) compared with $385,000 (21 cents) in the same period last year as sales rose to $53 million from $42 million.

Sales in the first half of Dart's current fiscal year were up more than 20 percent to $99.7 million compared with $80.6 million in the 1977 period.Profits were $956,000 (52 cents) vs. $267,000 (15 cents).

Planning Research Corp., a Washington firm that is the nation's largest professional services business, reported that profits jumped 27 percent in the year ended June 30.

Net income was $4.9 million (72 cents a share) compared with $3.9 million (60 cents) as revenues rose to a record $223 million from $186 million.

PRC sells information services, management consulting, planning and engineering services to business and government from 208 offices in 41 nations.

Flow General Inc., a diversified manufacturing and services company in McLean, also reported record sales and profits for the year ended June 30. The announcement yesterday came in the wake of unusually heavy trading in Flow General stock on the American Stock Exchange in recent days.

Earnings rose 42 percent to $1.63 million ($1.05 a share) from $1.15 million (87 cents) in the previous year, with more shares currently outstanding. Sales were up 16 percent to $49 million.

The Northern Virginia company, which issued a statement earlier this week that dismissed rumors of a potential merger as groundless, manufactures and sells biological products and broadcasting equipment.