T. Rowe Price Associates Inc., the Baltimore-based investment and mutual fund management firm, reported a 41 percent increase in its earnings in the third quarter. But that was before the recent steep drop in the stock market, which the company said it expects to have "an adverse impact on fourth-quarter results."

The firm said it earned $6.8 million (92 cents a share), compared with $4.8 million (65 cents) a year ago. Revenue rose 15 percent, to $33.8 million from $29.4 million. The company attributed the increases in the quarter, which ended Sept. 30, to the steady rise in stock prices that ended with last month's plunge. In addition, the company said, the higher stock values helped the company's asset-management fees.

For the nine months that ended Sept. 30, the company said its profit rose 37 percent, to $15.7 million ($2.13) from $11.5 million ($1.55). Revenue rose 21 percent, to $99.4 million from $82.1 million.

Although the company said it expects its overall results for 1987 to be healthy, it predicted poor results for the fourth quarter -- traditionally T. Rowe Price's weakest period for earnings -- because of the stock market drop.

"The recent sharp downturn in the equity market, plus above-average exchange activity out of our stock mutual funds into money-market funds, have resulted in a drop in equity assets under management," George J. Collins, the company's president, said in a statement. "The lower equity market will have an adverse impact on fourth-quarter results."

Hadron Inc., a Fairfax-based computer and services firm, said its second-quarter profit rose 8 percent, to $332,358 (2 cents a share), from $308,182 (2 cents) a year ago. Revenue rose 12 percent, to $6.7 million from $5.9 million.

For the first six months of the year, Hadron earned $716,394 (5 cents), up 28 percent from $558,041 (4 cents), a year ago. Revenue for the period rose 20 percent, to $13.4 million from $11.2 million.

Flow General Inc. losses continued to mount in the first quarter of fiscal 1988, which ended Sept. 30. The McLean company reported a loss of $868,000 (10 cents a share), compared with a loss of $463,000 (5 cents) in the year-ago quarter.

Flow General's revenue for the period totaled $54.2 million, a 15.1 percent increase from the $47.1 million in the same quarter last year.

Flow General officials said they anticipated the loss. "A first-quarter loss is normal for Flow General, and a loss of this magnitude was anticipated in our annual operating plan," said Robert E. Wenger, president and chief executive of the biomedical and electronics company.

But all "vital signs seem to be progressing well, and we expect to be profitable for the full fiscal year 1988," he said.