Penril Corp. has set Friday as the new deadline for its bondholders to accept a swap of debt for company stock and securities as an alternative to the troubled Maryland electronics firm's filing for bankruptcy.

The company is almost $2 million behind in interest payments on its $18 million debt. Under the terms of the offer, creditors can trade in the defaulted bonds for a combination of two classes of securities, or a combination of securities and common stock.

Gordon Hamlet, Penril's corporate controller, said that if at least 90 percent, or $16.2 million, of the bonds are not exchanged, the company may find it necessary to seek the protection from creditors with a bankruptcy filing.

By yesterday , approximately $11.2 million of the bonds had already been handed over for the exchange, and two other creditors, holding an additional $4.8 million in Penril bonds, had promised to accept the exchange offer.

Hamlet said that if the offer was not completed by Friday, Penril would probably extend the deadline for another week. Since the original offer was made on June 25th, the firm has made five such extensions.

The first class of securities offered to bondholders is unsecured notes with a $500 principal and staggered rates of interest rising to 12 percent by the time the notes are due in April of 1992. The second class includes unsecured notes with a principal of $650 and an option to buy 50 shares of Penril stock.

This is the third consecutive year of financial travail for the 19-year-old Rockville electronics company. After recording profits of $2.5 million for the fiscal year ending in July 1984, Penril's net income dropped to $39,000 the following year, before the company lost $11.8 million dollars last year.

The trend has continued into this year, with the company reporting a net loss of $3.6 million on revenues of $41 million for the first nine months.

The losses follow an aggressive corporate strategy that saw the firm buy 15 electronics companies between 1973 and 1985.

"That kind of acquisitional program is nice if it works," says David Beeghly, a financial analyst with Chesapeake Securities Research Group in Towson, "but often it doesn't. If you buy five used cars, chances are one is going to be a lemon."

Penril officials declined to comment on the firm's plans, but the company is thought to be looking for buyers for at least three of its unprofitable divisions, including Triplett, an electrical instruments manufacturer acquired in October 1983, and Alltest, an automotive electronic analysis business bought by Penril in 1985 for $3 million.

In a report to shareholders last year, Alva T. Bonda, chairman and president, said that Alltest's problems stemmed from a lack of "manufacturing capability." The company's Network Products data communications business was also identified as suffering from a similar problem.

"If they could get rid of Alltest and Triplett that would be a major help," says Beeghley, but he adds that that may be difficult, considering the amount of restructuring the two businesses will need.

Last November Penril sold two consumer products subsidiaries -- Epicure Products Inc., which makes high-fidelity speakers and turntables, and Concord Systems Inc., which makes automobile sound systems -- for $11 million, mostly in cash.