Alex. Brown Inc. reported yesterday that its profits doubled for the quarter ending March 28, with earnings climbing to $6.6 million (85 cents a share) from $3.3 million (48 cents) during the same time period a year ago.

The Baltimore investment company that went public in February, attributed the steep increase in profits to the rising securities market, strong trading activity and high levels of equity underwritings. "As a result, Alex. Brown realized increased results in virtually all areas of its business," said President Donald B. Hebb Jr.

However, Hebb warned, " . . . This quarter's results should not be considered indicative of the results to be expected for any other quarter or for the full fiscal year," which ends in September.

For the first six months of Alex. Brown's fiscal year, the company earned $10.1 million ($1.38) on revenue of $116.7 million. During the same period last year, it earned $6.2 million (91 cents) on revenue of $84.3 million.

*Schwartz Bros. Inc. posted a profits of $767,000 (95 cents a share) for its fiscal year that ended Jan. 31 -- nearly four times the $195,000 (24 cents) earned the previous year.

Revenue for the regional distributor of videocassettes, compact discs, records and audiocassettes increased by 52 percent to $64.5 million from $42.4 million the previous year. The company is based in Lanham.

Schwartz officials attributed the sharp rise to the surge in sales of prerecorded videocassettes and the expansion of its geographic market.

*Danaher Corp., the Washington holding company of industrial products controlled by brothers Mitchell P. Rales and Steven M. Rales, posted a 16 percent increase in profits for its first quarter, with earnings of $2.7 million (26 cents a share). First quarter 1985, earnings were $2.3 million (23 cents).

The increase in profits came despite a 4.7 percent drop in revenue from $70 million last year to $67 million this year. The decline was due entirely to the sale of a division of Mohawk Rubber Co., company officials said.