Washington Real Estate Investment Trust yesterday reported a 25 percent increase in first-quarter earnings, which the B. F. Saul REIT reported a sharp increase for the six months ended March 31, as area real estate trusts continued to show renewed strength despite soaring interest rates.

WRIT posted net income of $896,220 (20 cents a share) in the January-March period, compared with $732,511 (16 cents) a year earlier. Funds provided from operations rose to $1.27 million from $1.11 million, and trustees voted a regular quarterly dividend of 25 cents a share, payable June 30 to owners of record June 5.

The Bethesda trust attributed the gains to higher rental income and profits at three major properties -- office buildings at 1901 Pennsylvania Ave. NW. the GBS Building in Rockville and the State National Bank building in Kensington. Shopping centers in Westminster, Md., and Woodbridge, Va., also had much higher incomes.

WRIT recently sold 275,000 new shares at $16.25, and a company announcement yesterday said the trust is actively seeking new real estate investments.

The B. F. Saul trust said earnings for the six months ended March 31 rose to $5.2 million (88 cents a share) from $546,000 (9 cents) a year ago. Cash flow from operations was $9.4 million compared with $2.8 million, primarily because of profits from condominium conversions.

In the January-March quarter, net income was flat at $1 million ($17 cents) in 1981 and 1980, but cash flow from operations (prior to mortgage principal payments, and generally regarded as a good test of REIT performance) rose to $2.57 million from $1.95 million. The cash-flow gain was attributed to a $242,000 improvement in income-producing properties.

The Saul trust also noted that the gains would have been greater without an increase in the prime lending rate of banks of 2.7 percentage points between the two periods. Saul REIT will pay a dividend of 5 cents a share, payable July 15 to owners of record July 1.

Last week, another major area trust, Federal Realty of Chevy Chase, announced that its first quarter produced a 53 percent increase in first-quarter cash flow.

Riviere Realty Trust also reported a sharp turnaround, with $61,310 in funds from operations in the first quarter, compared with a loss of $234,467 in the 1980 period. Net income was $103,878 (13 cents a share), compared with $597,498 (76 cents) a year ago; the 1981 results included a capital gain from selling the Marlow Heights Bowling Lanes. President David Hoster II forecast a steady improvement in earnings for 1981.

Earning reports from other area corporations included:

Kay Corp., a retail jewelry and international trading company in Alexandria, reported a net loss of $5.7 million in the first quarter, compared with a loss in the 1980 period of $5.9 million. Revenues declined to $194 million from $246 million.

VSE Corp. of Alexandria reported earnings in the first quarter of $303,200 (41 cents a share), compared with $78,500 (11 cents) a year ago. The engineering and technology company's revenues rose to $11.2 million from $10 million.

Government Employees Financial Corp., a Denver-based consumer finance affiliate of Geico Corp., reported first-quarter profits fell sharply to $69,218 from $236,301 a year earlier. Although down from last year during an era when the costs of borrowing money were at record levels, the report did represent a turnaround after unprofitable operations in three prior quarters.