Primark Corp., the McLean holding company, said yesterday that it lost $5.9 million in the third quarter, compared with a $1.5 million loss in the same quarter last year.

The company blamed the results on investment losses, start-up costs for two new lines of business and losses at a business it sold within the quarter.

Primark's third-quarter revenue was $7.1 million, up from $6.1 million last year.

More than two years ago, Primark sold its Michigan Consolidated Gas subsidiary. It is interested in buying more businesses, but most of its assets are still in cash and stocks.

"The value of our equity investment holdings decreased with the overall drop in the market," said Chairman Joseph E. Kasputys. That decline, he added, "will help our acquisition program by allowing us to buy good businesses at lower prices."

Primark's new aircraft maintenance and electronic medical claims processing subsidiaries cost it $1.4 million in start-up costs in the quarter. Also during the quarter, it sold its Health Information International subsidiary, which increased its net loss.

GRC International Inc. of Vienna reported a $681,000 profit for the quarter ended Sept. 30. That compares with a loss of $394,000 in the same quarter last year. Revenue was $30.3 million, up 6.5 percent from $28.5 million last year. GRC, which until last year was called Flow General Inc., provides research and analysis services, mostly to the Pentagon.

Biospherics Inc. of Beltsville lost $23,489 in the third quarter, compared with a loss of $116,075 a year ago. Revenue rose 16 percent to $4.3 million from $3.7 million. Biospherics specializes in environmental services and biotechnology.