CSX Corp., a Richmond holding company for the Chessie and Seaboard Coastline railroad systems, reported a substantial increase in first-quarter profits on a 13 percent gain in overall revenues.

Earning were $87.8 million ($2.14 a share) in the January-March period compared with $55.1 million ($1.41) for the combined Chessie System and Seaboard Coastline Industries in the same quarter last year. The companies were merged formally on Nov. 1.

Revenues rose to $1.3 billion from $1.2 billion with transportation revenues up to 12 percent and nontransportation revenues up to 18 percent. CSX properties include substantial timber and mineral holdings, Florida newspapers and the Greenbrier resort in West Virginia.

CSX said the results reflected a relatively mild winter, the success of continued cost-control measures and strong export coal shipments. During the first quarter, export coal dumpings by CSX were 8.4 million tons, or 31 percent more than handled in the same period last year. Total coal movements for the quarter rose 21 percent to 59.2 million tons.

Systematics General Corp., a Falls Church developer and manufacturer of computer terminal devices and technology systems, reported sharp gains in sales and profits during 1980. Profits were $611,000 (44 cents a share) compared with year-earlier losses of $370,000 as sales jumped 45 percent to $11.3 million.

In the fourth quarter alone, SGC sales were up 24 percent to $2.9 million as the company recorded a loss of $2,000 compared with earnings of $356,000 (26 cents).The loss was attributed to inventory adjustments. At the end of the year, Sgc had a contract backlog of $3.8 million.

Separately, the firm announced a $1.6 million contract with the Naval Sea Systems Command to provide technology services.

Hotel Investors Trust and Hotel Investors Corp. of Kensington yesterday reported combine profits of $1.3 million (67 cents a share) in the second quarter ended Feb. 28 compared with $994,000 (58 cents) a year ago. Six-month earnings rose to $2.7 million ($1.41) from $2.5 million ($1.45).

The trust, which also declared a quarterly payout of 70 cents a share (on May 1 to owners of record April 15), invests in hotel properties. The corporation leases hotel properties of the trust, and shares of beneficial interest in the trust and stock of the corporation are paired and traded as units on the American Stock Exchange.