Profits of International Bank of Washington declined substantially in the third quarter and first nine months of 1981, largely because of funds set aside for possible loan losses at an unidentified Far Eastern subsidiary.

IB, a diversified financial services and merchant banking company based in the District, reported yesterday that third-quarter profits fell to $687,449 (5 cents a share) from $2.8 million (23 cents) in the same period last year.Nine-month profits declined to $7.2 million (57 cents) from $10.5 million (86 cents) a year ago.

Revenues in the recent nine months, including IB's equity interest of $3.6 million in the earnings of Foster Wheeler Corp., were $14.5 million compared with $18.2 million in the 1980 period.

IB said 1981 results reflect establishment of a $2.9 million reserve provided by a Far East subsidiary for possible loan losses. The reserve was made necessary "by the loss and decline in value of collateral securing "certain loans to this subsidiary's customers," according to an IB statement.

In addition, the Washington firm said it has provided financial assistance to this subsidiary "with the effect that there is no impairment of the subsidiary's capital." IB spokesman George Ureke said he could provide no additional details on the subsidiary involved. Among Far East operations are Reid Trading Co. Ltd. and IB of Washington (Far East) Ltd., both of Hong Kong. The latter, a bank, was acquired by the D.C. firm in 1974.

IB has operations or investments in 50 states and 38 foreign countries, including part ownership of industrial firms, insurance, finance and leasing, administration of Liberia's maritime operations and commercial banking outside the United States.

Bowl America Inc., a Springfield-based operator of 26 bowling alleys in Maryland, Virginia and Florida, reported a net loss of $30,761 for the first quarter of its fiscal year, down from a loss of $85,813 in the same quarter a year earlier. The company said it usually loses money in the summer quarter because of the "seasonal nature of the bowling business."

Gross receipts rose to $3.15 million in the 13 weeks ended Sept. 27 from $2.84 million in the 13 weeks ended Sept. 28, 1980, which the company attributed to higher food and beverage receipts and increased play on electronic-game machines as well as more games bowled.

Owens & Minor Inc., a Richmond wholesaler, reported that its second-quarter profits jumped to $661,000 (76 cents a share) from $424,000 (50 cents) in 1980. Owens & Minor said the increase was due to sales of inventories purchased at unusually low prices in a recent acquisition. Sales increased to $51 million from $37.5 million for the three months ended Sept. 30.

First-half sales increased to $93.5 million from $72.5 million, and earnings jumped 128 percent to $1.54 million ($1.78) from $673,000 (79 cents). The company said the extraordinary inventory profits added 76 cents to first-half earnings.

HGIC Corp. of Richmond, the parent of Home Guaranty Insurance Corp., said profits plunged to $20,000 (one cent a share) from $98,000 (10 cents) for the third quarter but increased to $290,000 (17 cents) from $221,000 (23 cents) for the first nine months of its fiscal year. Earnings per share did not parallel total earnings because of the sale of additional stock.

Profits for the third quarter ended Sept. 26 slipped at Doughtie's Foods Inc. of Portsmouth to $137,000 (18 cents a share) on sales of $11.8 million to $189,000 (25 cents) on sales of $11.5 million in the same period a year ago. Nine-month profits were $403,000 (53 cents), down from $419,000 (55 cents), while sales increased to a record $34 million from $32 million.

Biospherics Inc. of Rockville, a scientific and technology firm, reported a third-quarter net profit of $44,113 (2 cents a share) against a loss of $51,819 in the same period a year earlier. Revenue rose to $1.65 million from $1.49 million.

Nine-month profits were $101,255 (5 cents) against a loss of $18,182 in the same period of 1980. Revenue was $4.6 million, up from $4.4 million.

Riviere Realty Trust of Washington reported "significant improvement" in earnings from operations for the third quarter and for the first nine months of 1981. Net income for the quarter was $74,664 (10 cents a share), up from $1,685 in the year-earlier period.

Funds from operations, including the trust's properties in Indianapolis, were $239,924 for the quarter, up from $161,669 a year ago.

Nine-month net income was $226,255 (28 cents), down from $352,545 (45 cents) a year earlier. Funds from operations were $508,692 compared with a deficit of $169,413 a year earlier.

Computer Network Corp. of Washington, which incurred a net loss of $64,000 in the second quarter of its 1980 fiscal year, reported a strong comeback, with net income of $212,000 (12 cents a share) in this fiscal year's second quarter ended Sept. 30.

Revenues for the quarter were down substantially, however, to $3.298 million from $5.2 million a year ago. The revenue reduction was attributed mainly to the expiration of a contract with the U.S. Environmental Protection Agency.

First-half net income was $192,000 (10 cents) compared with a $172,000 loss a year ago, with revenues of $6.175 million for the most recent six months, down from $9.99 million a year earlier.