MCI Communications Corp. yesterday said 1985 earnings increased 91 percent to $113.3 million (48 cents) on revenue of $2.5 billion, up from $59.2 million (25 cents per share) on revenue of $1.9 billion a year ago.

Bell Atlantic Corp., Planning Research Corp., A. H. Robins Co. and Security National Corp. all reported increased earnings, while Black & Decker Corp. said profits declined.

In the fourth quarter ended Dec. 31, MCI, a Washington communications company, reported earnings of $8.3 million (4 cents) on revenue of $721.4 million, down from earnings of $13.2 million (6 cents) on revenue of $521.5 million for the same period last year.

MCI spokesman Gary Tobin said the company would have reported earnings of 15 cents per share in the fourth quarter except for an extraordinary cost of $26.3 million associated with recalling high interest-rate debt to avoid future high interest payments.

MCI said the overall upsurge in earnings was attributable to an increase in subscribers to MCI's Dial One long distance service.

*Bell Atlantic Corp. reported an increase in earnings of 12.3 percent for the year to $269.7 million ($2.69) on revenue of $2.3 billion, compared with 1984 earnings of $241.4 million ($2.43) on revenue of $2.1 billion.

*Planning Research Corp., a technology-based professional services company, said earnings increased slightly in the second quarter of fiscal 1986 ended Dec. 31 to $1.7 million (27 cents) on revenue of $114.8 million, compared with 1985 second-quarter earnings of $1.6 million (25 cents) on revenue of $81.7 million. Earnings for the first six months of 1986 were $3.9 million (59 cents) on revenue of $219.6 million, a 70 percent increase over earnings of $2.3 million (35 cents) on revenue of $159.9 million for the same period last year.

*Black & Decker Corp. reported first-quarter net earnings of $20.9 million, a decrease of 28 percent from the $29 million earned in the same period last year.

The power tool and small appliance maker's sales for the period were $521.7 million or 4 percent higher than in the first quarter of fiscal 1985. Earnings per share were 41 cents compared with 57 cents for the same quarter last year.

*Security National Corp., the parent of Security National Bank, said that it had record growth in 1985, with earnings rising 14.3 percent.

The bank holding company, which plans to merge with Bank of Virginia, said earnings for the year were $3.6 million ($3.85 a share), up from $3.1 million ($3.38) in 1984.

Net income for the fourth quarter was $938,000 ($1.02 a share), up 57.6 percent from $595,000 (65 cents) in the same quarter a year earlier.

*A. H. Robins Co. of Richmond said it posted a 1985 fourth-quarter profit of $13.5 million (55 cents a share) after losing more than $481,800 in the same period of 1984.

The net-earnings gain helped the company post an annual profit of $75.8 million ($3.12) in 1985, compared with a net loss of more than $461 million in 1984. Fourth-quarter sales were $186.1 million, compared with $166.2 million for the final quarter of 1984.

In August, Robins filed for financial reorganization under Chapter 11 of the U.S. Bankruptcy Code, citing litigation costs from its Dalkon Shield birth-control device.

The company sought protection from its creditors after 15,500 lawsuits and claims stemming from the Dalkon Shield, which Robins stopped selling in the mid-1970s after women claimed it caused sterility, miscarriages and other injuries.

The company said expenses related to the lawsuits reduced 1985 pre-tax earnings by almost $15.6 million, and costs related to the Chapter 11 proceedings reduced 1985 pre-tax earnings by $7.2 million.

The pharmaceutical company said sales for the 12-month period ended Dec. 31 totaled $706.1 million, an increase of 12 percent over 1984.