Two unusual real estate transactions and a reduction in operating losses enabled Capital Mortgage Investments of Chevy Chase to report a profit for the first three months of the year.

The troubled real estate investment trust said net income for the three months ended March 31 was $818,000 (49 cents a share) compared with a loss of $1.3 million (79 cents) in 1977.

The operating loss fell from $2 million to $270,000 before extraordinary items of $1 million this year and $1.3 million last year.

Capital Mortgage realized a $742,000 gain by accepting $2.1 million of its 6.5 percent debentures as payment for a defaulted mortgage.

John Wolf, vice president and treasurer, said the REIT is considering reacquisition of more debentures in exchange for mortgages or nonearning assets. The Capital Mortgage debentures have been selling at discounts of as much as 40 percent, but could become more valuable if the company continues to accept them.

Capital reported another $346,000 gain by giving its banks properties worth $1.8 million in exchange for reduction of debts, and said it has made more such deals since the quarter ended.

The REIT has reduced its debt from $57 million to $38 million in the past year, but said it is now in default of its bank lending agreement because its capital has fallen about $350,000 below the $12 million level required by the agreement. A waiver has been asked.

Financial Security Group Inc., the property and casualty insurance arm of International Bank, reported that first-quarter earnings increased 75 percent, from $1 million (35 cents a share) to $1.8 million (53 cents).

Operating income increased from just over $1 million to $1.5 million, and investment gains grew from $5,000 to $270,000.

The three Financial Security Insurance companies wrote premiums of $26 million, up from $23.8 million, and assets grew from $173 million to $176 million.

NUS Corp. of Rockville reported its first-quarter net income nearly doubled, climbing from $266,000 (27 cents a share) to $515,000 (52 cents) as revenues grew from $7.2 million to $10.2 million.

A spokesman said the gains were due primarily to growth in engineering and environmental operations of NUS, an energy and environmental consulting him.

Biospherics Inc., a Rockville research and consulting company, reported a loss of $9,000 (one cent a share) for the first quarter compared with a $47,000 profit (7 cents) last year.

The pre-tax loss of nearly $16,000 was reduced by income tax credits; Biospherics' revenues for the quarter increased from $536,000 to $632,000.

An investment of $54,000 in product development was the principal reason for the loss said President Gilbert.

Smithfield Foods Inc., a packer of hams and other foods based in Smithfield, Va., reported its quarterly income jumped from $447,000 to $4.4 million, including profits from sale of a subsidiarly and a $1.2 million tax credit.

Smithfield sold its Family Fish Houses subsidiary to the Macke Co. of Washington earlier this year, a transaction that produced a $2.7 million gain.

In April, the company settled an Internal Revenue Service claim for additional taxes for 1971 through 1975 of $2.3 million, producing a tax credit of about half that amount, $1.2 million.