Washington Home Corp. of Waldorf yesterday explained why it is one of the highest fliers in the two-month-old stock market boom with the release of its quarterly earnings, showing profits of $361,766 compared with a $273,078 loss in the same period last year. The net in the quarter was equal to 30 cents a share.

Chairman and Chief Executive Officer W. J. Harnett said the company, which builds low-cost houses throughout Maryland, is "benefiting greatly because of the drop in interest rates" of about six weeks ago, when FHA and VA mortgages fell to 12 1/2 percent.

The FHA mortgage rate dropped to 12 percent last week, and Harnett said his company sold 25 houses Sunday. "There's a lot of demand out there," he said. "People have been shopping. They know the homes they want. Now they can finally afford them."

As a result of the spurt in sales, Harnett said Washington Home is now seeking 20 new employes, largely construction workers and people to lay out developments. It is the first time in 2 1/2 years Washington Home has been hiring, and Harnett said it feels good.

Yesterday's earnings report on the company's first quarter ending Oct. 31 was issued earlier than usual at the request of the American Stock Exchange, which wanted to know the reason for the surprisingly high volume of trading Thursday and Friday. The stock zoomed 522 percent between August and last week -- from 1 1/8 to 7. It closed yesterday at 8.

Harnett said new orders are up 803 percent -- to $14,009,496 from $1,551,563 at the same time last year. Sales for the quarter were $6.2 million compared with $3.1 million last year.

Other real estate firms in the Washington area also reported improved profits yesterday.

The Rouse Co. of Columbia said its third quarter profits increased to $1.5 million (10 cents a share), compared with $495,000 (3 cents) for the same period in 1981. Earnings for the nine months that ended Sept. 30 increased to $5.2 million (35 cents a share) from $4 million during the first three quarters of last year.

The company pointed to successful openings in August of retail centers in New Jersey and Milwaukee and reported a 20 percent increase in their earnings over the nine months that ended Sept 30. During the third quarter, retail-center earning jumped 21 percent.

Washington Real Estate Investment Trust reported third-quarter profits of $1.2 million (26 cents) compared with $1.1 million (23 cents) in the third quarter last year. Profits in the first nine months of the year also increased, to $3.6 million (74 cents) from $3.2 million (68 cents). Sales in the quarter were $3.6 million, compared with $3.3 million last year, and for the nine months, sales grew to $10.6 million from $9.6 million.

Another area firm, LogEtronics Inc. of Springfield reported increased revenues for the first nine months of 1982, rising to $29 million from $24 million last year. Revenues in the latest quarter slipped to $7.9 million from $8.6 million in 1981.

The company reported a loss of $1.5 million during that period, compared with profits of $1.7 million ($1.41) the year before. For the latest quarter, LogE lost $1.7 million, compared with earnings of $269,000 (23 cents) last year. The company cited a $1.8 million provision for shutting down its graphic arts camera manufacturing operation.