Continued strong gains in aerospace operations kept Martin Marietta Corp. from showing the ill effects of inflation on its 1981 balance sheet, Chairman and Chief Executive J. Donald Rauth said yesterday.

Marietta, a diversified industrial products firm in Bethesda, reported earnings for 1981 of $200.07 million ($5.39 a share) on sales of $3.29 billion compared with earnings in 1980 of $188.13 million ($5.03) on sales of $2.619 billion.

For the fourth quarter, the firm said earnings were $38.65 million ($1.08) on sales of $860.47 million compared with earnings of $43.49 million ($1.16) on sales of $711 million a year before. The per-share figures reflect a 3-for-2 stock split during the fourth quarter of 1981.

Rauth said that the 1981 results were heavily dependent on "continued strong gains in aerospace." On the negative side, the recession hit other Marietta companies, particularly the firm's aluminum company. "Economic recovery is the 1982 key for the rest of our enterprise, particularly in aluminum," he said.

Baltimore Gas and Electric Co. reported net income applicable to common stock of $123.24 million ($3.70) for the year ended Dec. 31, 1981, compared with $117.3 million ($3.64) the year before.

Total net income was $149.66 million in 1981 compared with $139.39 million the year previous, and revenues were $1.421 billion compared with $1.226 billion.

Net income applicable to common stock was $17.21 million (51 cents) on revenues of $356.06 million for the last quarter of 1981 compared with $20.63 million (63 cents) on revenues of $303.55 million in the final quarter of 1980.

Total sales of electricity in 1981 rose by 2.1 percent over the year before because of a 5.1 percent increase in industrial sales. Cooler weather this summer helped keep residential sales approximately the same level as the year before, and commercial sales declined 1.9 percent.

Pargas Inc. of Waldorf, Md., reported net income of $13.15 million in 1981 ($3.62) on revenues of $281.21 million compared with $11.042 million ($3.03) on revenues of $273.69 million the previous year. The per-share figures reflect provisions for dividends and preferred shares.

Pargas, a distributor of liquefied petroleum and equipment for its use and storage, had net income for the fourth quarter of $5.4 million ($1.49) compared with $4.048 million ($1.12) in the fourth quarter of 1980.

Total volume of liquefied petroleum gas marketed during 1981 increased, the company said. Conservation in some areas was offset by increased sales for use as a motor fuel and because of the company's trading operation, according to representatives of the firm.

Ryland Group Inc., a Columbia-based home builder, reported earnings of $3.02 million (99 cents a share) compared with earnings of $6.57 million ($2.12). Sales were $230.88 million, down 18 percent from $258.04 million a year before.

Fourth-quarter earnings were $565,000 (19 cents) compared with $2.16 million (69 cents) for the fourth quarter of 1980. Sales were $53.74 million, down from $85.22 million.

C3 Inc., a Reston firm that is a custom integrator of minicomputer products and systems, reported net income for its third quarter ended Dec. 31 of $2.2 million (26 cents a share) on revenues of $13.2 million compared with $1.2 million (17 cents) on revenues of $8.4 million a year earlier.

Earnings for the first nine months of the company's fiscal year were $6 million (70 cents) on revenues of $35.1 million compared with earnings of $3.4 million (48 cent) on sales of $22.4 million a year before.