Bethesda-based Martin Marietta Corp. yesterday reported record 1978 first-quarter sales of $348 million compared with $309 million last year. Earnings for the period were $17.8 million (75 cents a share).

The company said the earnings also would have been a record except for a special, one-time lump-sum $14.8 million incentive award from NASA during the first quarter of 1977. That award ballooned quarterly earnings from 61 cents a share to 93 cents (for a total of $22 million).

The $14.8 million award was the maximum that could have been granted by the space agency for the company's work on Project Viking, the Mars exploration program, over a seven-year period.

The announcement came at the firm's annual meeting here - it's first session held away from corporate headquarters, which has been in Maryland since a move from New York City in 1974.

Chairman and Chief Executive J. Donald Rauth told some 75 shareholders that the "strong and favorable" first-quarter results were just the beginning of what he believed will be Martin Marietta's "best year ever."

The corporation reported financial improvements in all of its major interests, aluminium, cement, construction aggregates, specialty chemicals and aerospace industries, with several areas hitting record highs.

In a summary of operations, President Thomas Pownall said Martin Marietta Aluminum's improved performance last year came despite certain "negative influences." He cited a six-week strike at a Kentucky aluminum rodding mill and a drought in the Pacific Northwest that forced two smelters in Oregon and Washington State to cut energy consumption 15 percent. Both problems are now resolved.

Pointing to a 22 percent sales growth in aerospace, Pownall said "no single program dominates present and future sales," giving the firm protection against fluctuations due to overreliance on one project.

Rauth told the shareholders that the overall increases for 1977 over 1976, even including the extraordinary NASA award, were 18.5 percent for sales and 20 percent fore earnings. He said they show that the firm far out-distanced the generally accepted inflation factor of 6.2 percent.

And, Rauth said, two increases in the dividend in 1977 have resulted in the present dividend of $1.60 vs. $1.40 a year ago.

Rauth said the recently announced $213 million expansion plan was proceeding on schedule, calling it "a corporate vote of confidence" in the growing economy. Key areas of the expansion are in aluminum are aerospace where he said "several highly" specialized facilities are needed."

Rauth also commented on the firm's recent involvement in a takeover of Airco Inc., a large industrial company.

Airco had gone to Martin Marietta and other firms to see if they were interested in tendering an offer for control. Airco's move came when it appeared that BOC Industries was going to get some 80 percent of Airco's stock with a tender offer of about $43 a share. BOC orginally had told Airco that it wanted only 40 percent of the stock. Because of that, Airco sued BOC, contesting the takeover, and at the same time sought new buyers at a higher price.

Martin Marietta offered $50 a share for Airco, but BOC then matched the offer. Martin Marietta then pulled out. "We made what we considered to be a fair offer," Rauth said. "And we had no intention to enter a bidding contest."

However, Rauth added, "We are interested in a major acquisition on terms that are proper and favorable for Martin Marietta's long-term interests - which are growth and good levels of increasing profitability."

A shareholder's proposal to force it to publish a record of its political contibutions in several general-interest newspapers was defeated for the third straight year. The motion, offered by a company employe for absent corporate gadfly Evellyn Y. Davis, received 5.5 percent of the vote, down from about 7 percent last year.