MCI Communications Corp., citing the impact of telephone access charges on its long-distance service costs, yesterday reported a 71 percent decline in profits for 1984 despite a 29 percent rise in revenue.

Meanwhile, Dominion Resources Inc., Radiation Systems Inc., F&M Bancorp and Avemco Corp. reported earnings gains, while Eastmet Corp. said weakness in the stainless steel market was responsible for a widening of the company's losses to $13.8 million last year.

Washington-based MCI said the company's quarterly earnings "continued to be affected" by increases in access fees -- charged to long-distance carriers for use of local telephone lines. But it added that increases in its revenue base were allowing it to spread higher fixed costs more widely, a move expected to increase profits in coming quarters.

MCI's revenue potential is being enhanced by the continuing effects of last year's breakup of American Telephone & Telegraph Co., which allows telephone customers in an increasing number of cities to select a long-distance service from among AT&T, MCI and others. About 2 million Americans were allowed to make that choice last year, and more than 20 million Americans will be able to select their long-distance service this year.

"We expect strong revenue growth to continue with the increasing number of telephone customers who will have the option to select a designated long-distance carrier through the equal-access process during the next two years." MCI Chairman William C. McGowan said in a statement.

That outlook is marred, however, by the large number of phone customers who are choosing to stick with their AT&T long-distance service -- estimated to be as high as 90 percent in some areas. Of the rest, MCI is getting between 10 and 15 percent of the business, according to a company spokesman.

MCI said it earned $59.2 million (25 cents a share) last year, compared with $202.9 million (89 cents) in 1983, while revenue rose to nearly $2 billion from $1.5 billion in 1983. Fourth-quarter earnings fell 70 percent to $13.2 million (6 cents) from $43.6 million (19 cents) in the year-earlier quarter, despite a 21 percent rise in revenue to $521.5 million from $430.1 million.

In other recently released corporate results:

* Dominion Resources, the Richmond-based holding company for Virginia Power, said it earned $293.3 million ($3.46 a share) last year, a 10 percent rise from the $266 million ($3.28) it earned in 1983. It attributed the gain to lower overall expenses, including taxes and interest costs. Revenue was $2.6 billion during the year, up from $2.5 billion in 1983.

* Radiation Systems, a Washington-based maker of antennas for military and air traffic-control installations, said its earnings for the six months ended Dec. 31 rose 9 percent to $2 million (44 cents) from $1.8 million (40 cents) a year earlier. First-half sales rose 21 percent to $15.5 million from $12.8 million. The company said delays in receiving new orders had hurt results, but it expects to receive additional new business later this year to make up the shortfall.

In the second quarter ended Dec. 31, Radiation Systems earned $991,000 (22 cents), up 6 percent from $932,000 (21 cents) a year earlier. Sales increased 17 percent, to $8.3 million from $7.1 million.

* F&M Bancorp, Frederick-based parent of Farmers and Mechanics National Bank, said annual earnings rose 13 percent to $4.3 million ($5.84) from $3.8 million ($5.17), while fourth-quarter earnings climbed 24 percent to $954,300 ($1.28) from $765,600 ($1.03) a year ago. Deposits increased 11 percent last year to $302.3 million from $272.9 million at the end of 1983.

* Avemco, a Frederick-based company specializing in insurance for the aviation industry and other fields, said it earned $5.9 million ($1.97) in 1984, up 45 percent from $4.1 million ($1.50) in 1983. Annual revenue increased 27 percent to $47.7 million from $37.5 million.

In the last quarter of 1984, the company earned $1.8 million (60 cents), an 84 percent rise over 1983 fourth-quarter earnings of $979,000 (33 cents). Quarterly revenue increased 32 percent to $12.9 million, from $9.8 million in the fourth quarter of 1983. Avemco attributed the increases to business gained through the recent acquisitions of Eastern Aviation and Marine Underwriters Inc. and Matterhorn Bank Programs, a bank-insurance firm.

* Cockeysville, Md.-based Eastmet, a specialty-steel maker, said it lost $13.8 million in 1984, compared with an $8.2 million loss in 1983, as ebbing markets and rising costs buffeted the company. Sales increased 24 percent to $238.9 million from $192.2 million.

Much of the annual loss was posted in the fourth quarter, when the company was $8.8 million in the red on $47.4 million in sales. In 1983's fourth quarter, Eastmet had a $344,000 profit (7 cents) on sales of $61 million.

Last week, the United Steelworkers union approved a package of concessions for Eastmet's largest division, Eastern Stainless. It will significantly reduce the company's labor costs in exchange for a profit-sharing and stock-ownership plan.