Planning Research Corp. of McLean reported profits of $6 million (92 cents per share) for its fiscal year ended June 30, a 47 percent decline from earnings of $11.4 million ($1.62) the year before.

PRC, which provides engineering and information services, said its revenue increased to $372.4 million in 1985 from $320.7 million in 1984.

Fourth-quarter net income fell 15 percent to $2.3 million (36 cents) this year from $2.7 million (39 cents) in the year-ago period. Fourth-quarter sales increased to $118.5 million, from $84.9 million.

The company attributed the earnings decline to the depressed market for its engineering services, and an increase in interest and income expenses.

*Hazelton Laboratories Corp. reported earnings of $2.2 million (53 cents a share) for its fiscal year ended June 30, compared with a loss of $333,000 (8 cents) the previous year. The company, based in Vienna, Va., said this year's results include a net gain of $171,000 from discontinued operations, while last year's figures included a loss of $964,000 from discontinued operations.

Sales for the fiscal year increased to $55.9 million from $52.6 million the year before.

Fourth-quarter net income increased 203 percent to $660,000 (16 cents) from $218,000 (5 cents) in the same period last year. Sales increased to $15.3 million in the last quarter of this year from $13.7 million the year before.

Hazelton provides biological and chemical research services, makes laboratory and medical products and supplies research animals.