Martin Marietta Corp., the Bethesda-based defense contractor, said yesterday that its profit rose 7 percent last year, despite the $78 million it put aside in the final quarter to account for possible costs of a Pentagon delay in a major contract.

The company's net income in 1990 was $327.6 million ($6.52 a share), compared with $306.9 million ($5.82) in 1989. Its revenue was $6.12 billion, the company's highest ever, compared with $5.80 billion a year earlier.

In the fourth quarter, the company put $78 million into reserves to cover pre-production capital costs it has already incurred for the a new air defense system called ADATS. The Army has delayed for two years a decision on whether to move that system into full production.

The company said the reserve is intended to protect future earnings if the ADATS program is canceled. If the system is manufactured, the company said it anticipates recovering the cost. Analysts have estimated that ADATS could bring $4 billion to $6 billion in revenue to Martin Marietta over five years.

After accounting for that reserve, the company's fourth-quarter profit was down 22 percent, to $57.2 million ($1.17) from $73.5 million ($1.41) in the final quarter of 1989. Revenue in the quarter was down slightly to $1.56 billion from $1.62 billion a year earlier.

Mobil Corp. said its profit rose 7 percent in 1990, led by a sharp increase in fourth-quarter results caused by rising oil prices.

The Fairfax-based international oil company said it earned $1.9 billion ($4.60 a share) during the year, compared with $1.8 billion ($4.40) a year ago. Revenue for the company, the largest based in the Washington area, rose 14 percent, to $64.2 billion from $56.2 billion a year ago.

In the fourth quarter, the company earned $651 million ($1.58), up 46 percent from $447 million ($1.08) a year ago. Revenue in the quarter rose 30 percent, to $19.2 billion from $14.7 billion.

The sharp rise in crude oil prices caused by the crisis in the Persian Gulf was the chief reason for the improved results, Mobil said, although the company noted that its chemical operations continued to lose money in the quarter and year, and profit margins on its extensive refining and marketing operations were poor.

Mobil buys more crude oil than it produces, leaving its refining and marketing business vulnerable to raw-material price changes. The company has said it was not able to raise prices on gasoline and other products as quickly as crude oil prices rose and, as a result, its profit on U.S. refining and marketing operations fell more than two-thirds in the quarter and year. Higher profits in overseas refining and marketing offset those declines, however.

The company said its fourth-quarter profit was reduced by $145 million as a result of write-offs to cover revised estimates on the value of some assets.