The earnings information released Thursday by Communications Satellite Corp. and included in a Business section article yesterday contained only selected year-end results. The full earnings report will be released by Comsat later this month.

Communications Satellite Corp. yesterday released unaudited year-end results showing a decrease in income from continuing operations of $29 million in 1984 over comparable 1983 figures.

Comsat reported consolidated 1984 operating revenue of about $442 million, with consolidated net income of about $51 million and income from continuing operations of about $45 million.

The company said $13 million of the decline was attributable to a write-off associated with Satellite Television Corp., the direct satellite-to-home television company Comsat chose to cut back on.

Another $4 million is attributable to the write down of inventory from Comsat's equipment manufacturing business. The figures are preliminary estimates. The company will release final figures and per share earnings this month.

First Virginia Banks Inc. said its profit for the year increased 15 percent to $34.9 million ($2.44) from $30.4 million ($2.13) during 1983.

First Virginia's profit for the fourth quarter was up 20 percent to $8.5 million (59 cents) from $7.03 million (49 cents) during the same period last year.

Robert H. Zalokar, First Virginia's chairman, attributed the increase in earnings to the growth in earning assets, particularly loans, and to smaller increases in non-interest expenses than those experienced in the past several years.

Zalokar also said that 1984 income was affected by several non-recurring items. Earlier in the year, credits applicable to income tax adjustments for prior years were recorded in the net amount of $1.040 million, and during the fourth quarter, a gain of $791,000 was realized on the sale of one of the firm's office buildings. Losses of $311,000 were also incurred on the sale of investment securities by a nonbanking subsidiary during the fourth quarter.

USF&G Corp., a Baltimore insurance firm, reported that its earnings for the year dropped 98 percent to $4.32 million (8 cents), compared with $276.1 million ($4.86) in 1983.

During the fourth quarter the company lost $23 million, compared with profits of $118. 8 million ($2.20) during the same period in 1983.