MCI Communications Corp. said yesterday that its first-quarter earnings jumped more than sixfold over a year earlier largely because of a one-time gain related to the partial settlement of two lawsuits.

BellSouth Corp. said its first-quarter profit climbed 22.4 percent from a year earlier, while Bell Atlantic Corp. said earnings rose 8.5 percent.

MCI, a provider of long-distance telephone service headquartered here, said its profits surged to $40.4 million (17 cents a share), from $5.90 million (3 cents) during the same period last year. Revenue climbed to $570.6 million from $474.7 million a year earlier.

The company said its latest results included a $63 million gain on its settlement with US West Inc. of portions of two private antitrust suits against the former Bell System. US West is one of the regional holding companies spun off from AT&T.

MCI filed the lawsuits in 1974 and 1979 against the then-consolidated AT&T. Under the AT&T divestiture agreement, any damage awards are to be shared by AT&T and the seven regional holding companies.

MCI said its first-quarter results also included a $50.5 million write-off on equipment that performed pre-programmed dialing for certain long-distance customers. MCI said the equipment will become unnecessary as customers switch to a new dialing service being offered by the company. The year-earlier profit also had included an equipment write-off totaling $49.8 million.

* BellSouth, one of the seven regional holding companies formed to operate the 22 Bell system telephone companies divested last year from AT&T, said its first-quarter net income rose to $330.9 million ($1.10), from $270.4 million (93 cents) last year. Revenue increased to $2.50 billion from $2.27 billion.

The Atlanta-based company said its latest results included a one-time charge against earnings of $77.5 million resulting from a previously announced court-ordered refund of revenues that its South Central Bell unit had collected in Mississippi between 1982 and 1984.

Otherwise, the company "ended 1984 with improving performance, due in no small measure to extraordinary cost-control efforts, and that performance has been sustained during the first quarter of 1985," BellSouth Chairman John L. Clendenin said in a statement.

* Bell Atlantic, based in Philadelphia, said net income rose to $255.3 million ($2.56), up from $235.4 million ($2.44) a year earlier. Revenue climbed to $2.12 billion from $1.96 billion during the same period last year.

* Pepco reported net income of $34.8 million (66 cents) on revenue of $290 million, compared with $34.1 million (64 cents) on revenue of $264 million earned in the first quarter of 1984.

For the year ended March 31, earnings were $168.8 million ($3.25), compared with $151.5 million ($2.89) during the same period a year earlier.

Gannett Co. Inc., the media company, said that its net income for the first quarter increased by 19 percent to $41.3 million (52 cents), compared with $34.8 million (44 cents) a year ago. Revenue increased 14 percent to $482.6 million, compared with $425.2 million a year ago.

In the first quarter, Gannett announced an agreement in principle to purchase the Des Moines Register in Indiana and the Jackson Sun in Tennessee from the Des Moines Register and Tribune Co. Gannett also purchased Family Weekly magazine from CBS Inc., and in the outdoor division, Triangle Sign Co. of Chicago was purchased.

Black & Decker Corp. reported that its second quarter net earnings were down 36 percent to $14.7 million (29 cents), compared with $23.1 million (49 cents) during the same period last year. Sales for the quarter were up 26 percent to $403 milion, compared with $318.8 million during the same period last year.

Laurence J. Farley, president and chief executive officer, said, "The lower second-quarter results were expected and were largely due to a general retail distribution restocking slowdown in the United States, and continued adverse currency comparisons to last year." He also attributed the decline to higher promotion costs, particularly in the firm's household products group.

For the first six months, Black & Decker's net earnings were down 12 percent to $43.7 million (86 cents) on revenue of $906 million, compared with $49.8 million ($1.05) on revenue of $676 million during the same period a year ago.