Business for several of the largest Washington-based corporations remained at record levels in the first quarter of 1980, despite recessionary trends in the overall national economy, according to earnings statements released yesterday.

Southern Railway profits jumped 43 percent and were the highest on record for any three-month period in the company's history. Dynalectron Corp., meanwhile, reported earnings more than four times those of a depressed period last year and Financial General Bankshares Inc. reported the best first quarter in a decade.

Southern's first-quarter earnings were $51.2 million ($3.29 a share) compared with $35.8 million ($2.33) in the 1979 period as revenues jumped 19 percent to record $401 million. The previous quarterly record for profitability was $50.76 million in the second quarter last year.

L. Stanley Crane, the railroad's chairman, said yesterday that a higher volume of business coupled with higher freight rates contributed to the substantial gains. Revenue ton miles (one revenue ton carried a mile) increased by 8 percent in the quarter while freight rates increased 14 percent, including periodic adjustments to account for soaring fuel costs.

Of 12 leading categories of commodities carried on Southern freight cars, 11 contributed higher revenues. The exception was transportation equipment -- mainly new cars and parts -- which declined about 4 percent. Coal shipments soared 35 percent, Crane said.

However, Crane cautioned that freight carloadings in the last four weeks of the recent quarter had trailed those of the same weeks in 1979. "The high volume of business attained in last year's second quarter will be most difficult to duplicate in this year's quarter, particularly in an economy which increasingly is showing signs of slowing down," Crane asserted.

Operating expenses rose a sharp 18 percent in the recent quarter because of higher diesel fuel and wage increases. The cost of fuel along was up 45 percent to $45 million, he noted.

Dynalectron Corp., a McLean electrical engineering, aviation services and energy firm, said first-quarter profits rose to $1 million (14 cents a share) from $201,000 (3 cents) a year earlier.Revenues rose to $97 million from $75 million.

In a addition, Dynalectron announced yesterday that its backlog of orders and contracts at the end of the quarter was $325.5 million compared with $239.1 million 12 months ago.

Financial General Bankshares Inc., a Washington bank holding company whose officers revealed this week that they are talking about selling their stock to a group of Middle East investors, reported first-quarter operating earnings of $4.5 million (65 cents a share), up 43 percent from $3.2 million (46 cents) in the same period last year. Return on average assest rose to 1.03 percent for the quarter from 0.78 percent a year ago while return on shareholder's investiment increased to 14.1 percent from 11 percent.

President 4. William Middendorf II attributed the earnings gain primarily to an increase in net interest income of 18 percent, resulting from "higher levels of earning assets and higher interest rates, especially in the commercial loan area."

In addition, Financial General had a non-recurring after tax gain of $408,000 (6 cents) from the sale of an investment. Total loan volume for the company's banks jumped 11 percent to $1.28 billion. Financial General owns or controls 12 banks in D.C., Maryland, Virginia, New York and Tennessee including First American in D.C., Maryland and Virginia.

Central Fidelity Banks Inc., a Richmond bank holding company, and Dominion Bankshares Corp., a Roanoke bank holding compnay, also reported increased first-quarter earnings. Not counting gains or losses from selling securities, Central Fidelity earnings were a record $4 million (37 cents) compared with $3.7 million (66 cents) last year. Dominion earnings rose more slowly to $5.4 million (75 cents).

Central Fidelity assets rose 4.6 percent in the past 12 months to $1.74 billion while Dominion assets expanded by 10.5 percent to $2 billion. "We are pleased with these first quarter results in light of the chaotic financial climate of the period," said Dominion President Byron Hicks.

Atlantic Research Corp., a diversified rocket, research and communications manufacturing firm in Alexandria, reported first-quarter earnings were off to $307,000 from $354,000 a year earlier although sales increased to $13.8 million from $12.3 million. Per-share earnings were off more substantially, to 21 cents from 31 cents, because of more shares outstanding in the recent quarter.

New business bookings in the quarter were $30 million, increasing the backlog as of March 31 to $58 million from $36 million a year ago, Atlantic Research said.

United Services Life Insurance Co., a Washington firm that sells life policies to military officers and their families, reported a $3.4 million (65 cents a share) gain from operations in the first quarter, up 16 percent from $2.9 million (56 cents) a year ago. After capital gains or losses, net income was $3.3 million (65 cents) vs. $3 million (57 cents). Insurance in force rose to more than $7 billion, a doubling in the past decade.