Mortgage Investors of Washington has reported its first quarterly operating profit in six years, while Best Products Co., a Virginia catalogue retailer, said profits declined in recent months despite a substantial increase in sales.

In a separate report yesterday, Bowl America Inc. reported record profits for the second fiscal quarter ended Dec. 28.

Mortgage Investors of Washington reported an operating profit of $36,404 in the three monts ended Dec. 31, not counting gains from selling real estate or other unusual items. Major factors contributing to the operating earnings were additonal rents and interest from investments, a reduction in interest expenses from the refinancing of $15 million of notes last October and a gain on the repurchase of 10 percent of subordinated debentures.

An announcement by the real estate trust said significant progress has been made in returning the business to profitable operations. In another development, Peter Zwart, president of General Investment Management of The Netherlands, was elected chairman of the trust, replacing Floyd Davis Jr., who retired. The Dutch firm acquired a 51 percent interest in the trust last year.

Peyton Fletcher III also resigned as MIW prsident, and William Savage was named managing trustee and chief executive. In the six years sicne MIW last reported a quarterly operating profit, bank debts have been cut by more than $70 million and public debt has been reduced by $15 million, Savage noted.

Best Products, the nation's largest catalogue retail firm, said profits fell in the second fiscal quarter ended Dec. 31 to $17.9 million ($1.85 a share) from $20.5 million ($2.21) a year ago, even though holiday season sales boosted revenues by 15 percent to $442.5 million.

Six-month profits declined 17 percent to $20.3 million ($2.10) from $24.6 million ($2.65) as revenues rose by 17 percent to $629 million. Pretax profits declined from 8.6 percent of sales to 5.8 percent of sales because of lower profit margins and higher expenses in an era of tough retail competition. l

President Andrew Lewis blamed the unusual decline in profitability at Best's 89 stores on the lackluster sales environment, but he found several factors that were encouraging: "Our commitment to adjust quickly to a singificantly changed current retail marketplace was evidenced by better-than-budgeted control of expenses and reduced inventory levels"

Bowl America of Springfield said profits in the recent quarter rose to $491,620 (36 cents a share) from $443,045 (32 cents) a year ago as revenues rose to $4.36 million from $4.03 million. In the six months ended Dec. 31, earnings increased to $4ok,807 (30 cents) from $385,395 (28 cents), and revenues were up to $7.2 million from $6.8 million.

The company credited its newest bowling center in Burke as an important contributor to growth of revenues and profits, partly because the complex and equipment were financed with internal funds without the need to borrow at high interest rates. Bowl America now operates 26 centers in the Washington, Baltimore, Richmond, Jacksonville and Orlando areas.

C3 Inc. of Reston, a manufacturer of minicomputer products and systems that recently sold an initial offering of stock to the public, reported profits in the third fiscal quarter ended Dec. 31 of $1.2 million (34 cents a share) vs. $804,000 (23 cents) as sales rose to $8.3 million from $3.7 million. Nine-month profits rose to $3.4 million (95 cents) from $1.5 million (42 cents) as sales increased to $22.3 million from $7.8 million.

John Hanson Savings & Loan of forestville reported that earnings rose during the second fiscal quarter and six months ended Dec. 31, a period during which many thrift institutions operated at a loss. The stockholder-owned S&L posted second-quarter profits of $291,300 (25 cents a share) compared with a loss last year of $20,065. For the six months, John Hanson earned $435,290 (37 cents) compared with $238,797 (20 cents) a year earlier.

Chairman Charles Dukes Jr. said total assets rose 22 percent to $174 million, while deposits increased 25 percent to $146 million. He attributed the gains to aggressive lending practics at his 10 offices, among other factors. In addition, as a Maryland-chartered S&L, John Hanson is able to pay higher interest rates on passboodk savings accounts than federally insured S&Ls.