Penril Corp., a Rockville-based manufacturer of electrical equipment, is negotiating to acquire two other makers of electronic hardware that would almost double the size of the company's annual sales of $41 million.

Penril President Kenneth Miller said yesterday that, if the talks are successful, letters of intent to purchase companies with $10 million and $20 million in annual sales could be signed within the next two to four weeks.

"I would be disappointed if it was more than a month away on each," Miller said.

He declined to give specific details about the two companies involved, but said both are located outside the Washington area and would add between 550 to 600 employes to the company's 700-person work force.

Miller said Penril expects to pay about $13 million for the two companies. Most of the financing for the purchases would come from $11.5 million in credit available through Riggs National Bank at 17 percent interest, he added.

Spurred by a highly favorable article this week in Barron's, Penril's stock jumped more than a point yesterday to close at 8 7/8 on the American Stock Exchange. Demand for the stock was so heavy on Monday that Amex officials temporarily halted trading.

The Barron's article projected profits for Penril as high as $1.50 a share for the fiscal year beginning Aug. 1. Profits for fiscal 1982 should be close to $1.05 a share, Miller agreed.

"The $1.50 figure really grabbed people," said Stanley Lanzet, an analyst at Drexel Burnham Lambert who follows Penril.

Penril manufactures data communications equipment, test instruments, electronic power conversion equipment, and high-fidelity speakers for home and automobile stereo systems. It has facilities in Rockville, California, New York, Massachusetts, Connecticut and Switzerland.

The 14-year-old company has grown primarily through eight acquisitions of related electronics businesses.