Planning Research Corp., a professional services and consulting firm, yesterday reported net income of $1.06 million (15 cents a share) for the quarter ended March 31, compared with net income of $949,000 (14 cents) for the same period a year ago.

Income for the 1980 first quarter included a gain of $465,000 from an adjustment in a reserve that had been set aside for the corporation's Iranian operations.

1979 net income included a nonrecurring gain of $3.22 million and a nonrecurring loss of 598,000 on the sale of subsidiaries as well as a $2.5 million loss on the establishment of reserves for operations in Iran.

Washington Gas Light Company has announced that net income for the 12 months ended March 31 reached $17.59 million ($3.39 a share), up from $15.33 million ($2.85) for the year ended March 31, 1979.

A major factor in the improvement of earnings this year was higher retail rates, the company said. The company noted in a statement, however, that WGL is earning below the rate of return allowed by local regulatory commissions.

The increase in earnings was even greater before 1979 earnings were restated to reflect accounting changes that call for recording revenues applicable to unbilled gas.

Earnings for the 12 months ending March 31, 1979, before the change, were $10.92 million ($1.84).

The Washington Corporation reported that for the quarter ended March 31, the company had net income of $372,423 (16 cents a share), compared to net income of $230,707 (11 cents) for the same period in 1979.

The Washington Corporation, formerly Capitol Mortgage Investment, is a real estate investment company.

Monumental Corp. of Baltimore reported the corporation's consolidated operations after deducting dividends on preferred stock, amounted to $4.35 million (63 cents a share) for the first quarter of 1979.

The decline resulted from increased interest expenses to the corporation on funds borrowed to repurchase shares of its common stock and from a decline in the operating earnings of Monumental Life, a subsidiary, according to the company.