Communications Satellite Corp. yesterday said its third-quarter earnings decreased slightly to $12.5 million (68 cents a share) on revenue of $121 million from $12.7 million (71 cents) on revenue of $104 million for the same period last year.

Comsat, a Washington communications company, said nine-month earnings were $44.6 million ($2.45) on revenue of $362 million compared with earnings of $36.8 million ($2.04) on revenue of $304.7 million for the same period last year.

Comsat attributed the slight dip in earnings in the third quarter to unusually high interest costs associated with new construction. Comsat is trying to sell two satellites valued at $120 million. The company was going to use the satellites for the provision of a new satellite-to-home broadcast service that it folded.

The company's unusual interest expense was $3.9 million this quarter, which depressed earnings by 10 cents a share. The unusual interest expense is expected to be $9.9 million, or 32 cents a share, for the year, Comsat said.

* Ryland Group Inc., a real estate and mortgage company based in Columbia, Md., yesterday said its third-quarter earnings were up 122 percent over the same period last year.

Ryland reported income of $5.8 million (92 cents a share) on revenue of $148.2 million, up from $2.6 million (42 cents) on revenue of $113.1 million for the same period last year. Chairman Charles E. Peck said the increased income came from the sale of more mortgages and homes through subsidiaries Ryland Mortgage Co. and Ryland Homes.

* Maryland National Corp., the holding company for Maryland National Bank, reported third-quarter net income of $19.5 million ($1.00 a share), up 56 percent from earnings of $12.5 million (73 cents) the previous year.

Nine-month net income for the Baltimore company was $53.1 million ($2.83), up 48 percent from $35.9 million ($2.08) the year before.

Alan P. Hoblitzell Jr., chairman and chief executive officer, said the results reflected continued loan growth.

* Central Fidelity Banks Inc. of Richmond reported an 8 percent increase in third-quarter net income to $8.2 million (60 cents a share) from $7.6 million (58 cents) in the same period of last year. Nine-month profits increased 12 percent to $24.6 million ($1.81) from $22 million ($1.70) the year before.

Total assets as of Sept. 30 reached $3.4 billion, up 20 percent over the previous year.

Carroll L. Saine, chairman and chief executive officer, attributed the results to "continued growth in net interest income from a higher volume of loans outstanding and to continued significant increases in other operating income."

* VM Software Inc. of Vienna reported third-quarter earnings of $668,988 (16 cents a share), up 97 percent from profits of $339,244 (10 cents) the year before. Revenue increased to $4.3 million from $2.7 million.

For the first nine months, net income increased 60 percent to $1.6 million (41 cents) from $1 million (29 cents), while revenue rose to $11.7 million from $7.1 million.

VM Software made its initial public stock offering in May. The company develops, markets and supports system software products.

* Gray & Co. Public Communications International Inc., a public relations firm, reported profits of $400,561 (16 cents a share) for its second quarter that ended on Aug. 31, up 90 percent over earnings of $211,000 (9 cents) the year before. Revenue increased to $7.4 million from $4 million the year before.

For the first six months of the fiscal year, earnings increased 43 percent to $719,000 (29 cents) from $504,000 (22 cents) the year before. Revenue grew to $13.5 million from $7.5 million.