Sales at Black & Decker Manufacturing Co. were flat in the quarter ended June 28 while earnings rose 25 percent. For the first nine months of its fiscal year, however, the company reported an 8 percent earnings decline.

Sales for the quarter were $331.8 million versus $332.1 million last year, while earnings were $21.2 million (50 cents a share) versus $17.0 million (41 cents) for the equivalent period in 1980. For the nine months, earnings fell to $65.0 million ($1.54) compared to $70.5 million ($1.68) last year, while sales rose slightly to $1.12 billion from $1.11 billion.

The Towson, Md.-based tool company attributed the sluggish sales to depressed market conditions in Europe and continuing weakness in worldwide sales of the company's McCulloch chain saws. High interest rates also reduced earnings figures, the company said. On the other hand, new products met with strong sales.

Avemco Corp. announced record earnings for the second quarter of $800,000 (32 cents) versus $619,000 (24 cents) for 1980's second quarter. For the half, earnings were a record $1.94 million (78 cents), compared to $1.68 million (67 cents) last year.

Second-quarter sales for the Bethesda-based company rose to $7.93 million from $6.13 million last year, while sales for the half rose 27 percent to $14.91 million.

Avemco sells insurance, financial services and product marketing in aviation.

Computer Entry Systems Corp., an optical equipment manufacturer in Silver Spring, reported record sales and earnings for the second quarter. Net income rose to $376,000 (12 cents), compared with $255,000 (9 cents) for the same period last year. Sales stood at $2.01 million for the quarter, a big boost from $1.47 million last year.

For the first half, earnings rose 44 percent to $656,000 (22 cents) from $457,000 (16 cents) last year. Computer Entry went public on April 15 of this year.

First & Merchants Corp., a Richmond banking firm, reported second quarter net income of $3.64 million ($1.14), down 9.8 percent from $4.04 million ($1.24) last year. For the first half, net income was down 4.6 percent to $7.50 million ($2.31) versus $7.87 million ($2.41) last year.

Income before securities transactions for the quarter fell to $3.93 million for $4.14 million last year, while the results for the half showed a fall to $8.16 million from $8.23 million for the first half of 1980. The bank saw a slight fall in total average deposits, from $1.71 billion to $1.69 billion, while short-term deposits such as demand deposits, checking and NOW accounts rose a strong 8.4 percent.

Chairman C. Coleman McGehee said that results for the rest of the year should improve with stronger expected loan demand and lower interest costs for the money the bank has to take in.

First American Bank, a Washington-based subsidiary of Financial General Bankshares Inc., reported second quarter profits of $1.68 million (74 cents), up 8.9 percent from $1.54 million (68 cents) for the same period in 1980. For the first half, profits rose 8.4 percent to $3.37 million ($1.37 per share) the year before.

Assets for First American on June 30 were $674 million, while deposits were $528 million.

United Bank & Trust Co. of Maryland, based in Oxon Hill, reported record second quarter earnings of $169,119 ($1.54), compared with $130,377 ($1.19) for the same period last year. For the first six months, earnings were $321,637, up 23 percent from $261,587 last year. Assets on June 30 were $49.9 million, an 18.3 percent rise from $42.1 million last year.

The Washington Corp., a Chevy Chase-based banking firm, reported earnings for the second quarter of $901,170 (38 cents), up from $450,980 (20 cents) last year. For the first half, earnings were $1.05 million (45 cents), versus $823,403 (36 cents) last year.

Washington also said it had been formally notified that Berkeley Bio-Medical Inc., a San Francisco medical products firm, has acquired "just under 5 percent" of Washington's outstanding shares. Berkeley said it anticipates additional purchases, perhaps with an eye toward controlling the Chevy Chase company. Washington officials had no comment on the move, except to say that company "has previously adopted a policy that the company remain independent."

In another development, the bank reached an agreement with five banks to repurchase more than 468,000 Washington convertible preferred shares that the banks hold, at a price of $1.50 a share. The sale is contingent on the repayment of $4.48 million in loans to the five banks, and on other undisclosed events.

Women's National Bank announced profits for the first half of $131,000 ($1.31), an 82 percent increase over last year's figure of $72,000 (72 cents). Deposits rose 17 percent over the year to total $11.07 million on June 30. Total assets rose 35 percent, totalling $16.29 million.

Equitable Bancorporation, a Baltimore-based banking company, reported net income for the quarter ended June 30 at $2.59 million (62 cents), up 19 percent from $2.18 million (52 cents) last year. For the first half, profits rose 40 percent to $5.35 million (1.29), up from $3.83 million (92 cents).

For the quarter, income before securities losses fell 2 percent to $2.33 million (56 cents), from $2.36 million (57 cents) last year. Deposits at the end of the quarter stood at $1.66 million, a slight increase from last June's figure, while total assets rose 4 percent to $2.02 million from $1.95 million last June 30.

Arlington-based First Commercial Bank reported earnings for the first six months of $312,000 ($1.55), before securities transactions.

American Indian National Bank posted a record 45 percent earnings increase for the first half, with net income for the year-to-date totalling $465,319 versus $256,307 last year. Deposits on June 30 amounted to $24.12 million compared to $13.79 million last year, a 75 percent increase, which chief executive officer Conley Ricker attributed to the development of specialized banking services and increasing support from Native American groups throughout the country.

F&M National Corp., a Winchester, Va. bank, showed second quarter net income up 13 percent to $509,200 (30 cents), versus $574,600 (34 cents) this year. For the first six months, net income was $1.09 million (65 cents), up 6.3 percent from $1.02 million (61 cents) last year. Deposits on June 30 rose 6 percent to $189.5 million over the last year, and total assets increased 7 percent to $216.2 million.