Geico Corp., troubled by poor performance in its investment portfolio, yesterday reported a sharp decline in profits for the fourth quarter of the year and a small drop for the entire year, compared with 1989 results.

The Chevy Chase-based insurance company earned $208.4 million ($13.64 per share) for the year, down from $213.1 million ($13.74) in 1989, and $54.8 million ($3.64 per share) for the quarter, down from $80 million ($5.18) a year earlier. The figures represented declines of 2.2 percent for the year and 31.5 percent for the quarter.

Revenue for the year was about even at $1.9 billion. For the quarter, revenue fell 7 percent to $492.5 million from $528.1 million.

For the year, premiums climbed to $1.69 billion from $1.62 billion for 1989. Premiums rose to $440.9 million for the quarter from $416.3 million a year earlier.

Chairman William Snyder called the firm's results from insurance operations "satisfactory" and said they "compare favorably with 1989 results." He noted that while the severity of automobile claims continued to rise, weather-related catastrophe losses were "well below" those of 1989.

Communications Satellite Corp., citing one-time costs of restructuring its troubled video entertainment division, yesterday reported a loss for the final quarter of 1990, which translated into a loss for the year.

The fourth-quarter loss was $66.3 million, compared with a $7.6 million profit in that period in 1989.

Revenue for the quarter grew 16 percent to $116.8 million from $100.4 million.

For the year, District-based Comsat recorded a loss of $16.3 million, compared with a profit of $62.5 million in 1989. Revenue for the year expanded 11 percent to $456.8 million from $411.5 million.

Comsat's government-regulated core business of channeling satellite communications to and from the United States continued to expand during the quarter, with revenue rising 18 percent to $79.7 million from $67.8 million and operating profit rising 28 percent to $22.1 million from $17.2 million.

But the strong performance there was offset by continuing losses during the quarter in its video entertainment division, which reported an operating loss of $105.6 million. Most of that was due to a $97.6 million charge taken to restructure Comsat's business channeling pay movies into hotel rooms. The video unit laid off one-third of its 200 employees in January in connection with that.

Black & Decker Corp., the Towson-based toolmaker that has been digesting its 1989 acquisition of Emhart Corp., reported sharply higher profit for 1990.

Net income for the year rose 70 percent to $51.1 million (84 cents per share) from $30 million (51 cents) in its 1989 fiscal year. The company's 1989 results were dragged down by interest and other costs associated with the $2.7 billion Emhart purchase. (Because the company changed its fiscal year, the 1989 results are for the 12 months ended Sept. 24, while the 1990 results are for the 12 months ended Dec. 31.)

Revenue rose 50 percent to $4.8 billion from $3.2 billion. That included $607 million in revenue from Emhart companies, including PRC Corp., a McLean-based government services company. Those operations were not fully included in Black & Decker's financial statements until 1990's second quarter.

In the year's final quarter, net income was $6.8 million, compared with a loss of $3.2 million in the three months ended Dec. 31, 1989, which was a transitional period between the two fiscal years. Revenue rose 18 percent to $1.3 billion from $1.1 billion.