MCI Communications Corp., the D.C. company that competes with the Bell System's long-distance telephone service, more than quadrupled profits in the fiscal year, while more than doubling its revenue, the firm reported yesterday.

One of the largest companies in business history to double sales in a year, MCI reported net income for the year ended March 31 of $86.5 million ($1.81 a share) on revenues of $506.4 million. For the previous year, MCI reported net income of $21.1 million (24 cents) on revenues of $234.2 million.

On a quarterly basis, the figures are even more impressive. For the final quarter, net income was $33.8 million (70 cents) on revenues of $164.7 million, against net income of $7.9 million (11 cents) on revenues of $71.8 million in the same period a year ago.

MCI's profitability has escalated rapidly in recent years. Quarterly earnings on March 31, 1980, were $5.2 million; for March 31, 1981, $16.3 million. Operating or pretax income shot up from there to $59.2 million in the most recent quarter.

Wayne English, MCI's chief financial officer, attributed the performance to the fact that "we more than doubled our sales volume and kept good control over operating expenses." He said MCI has enjoyed a "steady, quarter-by-quarter improvement," and its profitability over the past year was not the result of any one transaction or set of market conditions.

MCI, still awaiting an appeals court judgment on its successful, $1.8 billion suit against American Telephone & Telegraph Co., argued aggressively for a break-up of Bell in the government's antitrust case against AT&T. In the proposed settlement of that case, MCI expects to gain equal access to local telephone networks.

In other D.C.-area earnings reports, Geico Corp. said its figures were essentially flat, but Federal Realty Investment Trust turned in an increase in profits.

Geico Chairman John J. Byrne, citing more frequent accidents, said net income for the first quarter, ended March 31, was $16.9 million (82 cents), compared with $16.4 million (75 cents) for the similar period last year.

Geico property and casualty premiums increased 9 percent to $171 million from $156.9 million last year, the company said.

Federal Realty's profits for the first quarter were $726,000 (37 cents), compared with $465,000 (24 cents) for the similar period of 1981.