Mobil Corp. and Getty Oil Co. reported yesterday that their first-quarter profits were more than double those for the same period a year ago.

And Sun Co. Inc. reported a 96 percent increase in first-quarter earnings.

Mobil, the second-largest U.S. oil company, said its estimated profits from operations totaled $922 million in the latest period on revenues of $15.3 billion. Total first-quarter earnings were $1.38 billion ($6.50 a share), including an after-tax profit of $459 million from the sale of Mobil's interest in Belridge Oil Co. to Shell Oil Co.

The operating earning were 105 percent above the figure of $449 million ($2.12 a share) a year ago. Mobil's domestic profits rose $109 million, or 57 percent, in the first quarter.

Sun Co. the 10th-ranked U.S. oil company reported earnings of $251.3 million ($4.17 a share) on revenues of $3.1 compared with profits of $128.3 million ($2.18) on revenues of $2.4 billion a year ago.

Getty reported first-quarter profits of $225.8 million ($2.75 a share), on sales of $2.26 billion. Earnings a year ago were $108.2 million ($1.31) on sales of $1.1 billion.

These jumps in earnings, like those reported earlier in the week by other oil companies, reflect the escalation of world oil prices, which have doubled to about $30 a barrel since the start of 1979. At the same time, President Carter's decision to phase out federal controls on U.S. oil has permitted a steady increase in domestic petroleum prices.

Oil company officials said the new federal windfall profits tax had a small impact on first-quarter profits, but would contribute to a decline in profits in the balance of the year.

The windfall tax took effect March 1. Had it been in effect the entire first quarter, Sun's profits would have been $16 million less, said Theodore A. Burtis, Sun chairman.

Mobil Chairman Rawleigh Warner Jr. said the first-quarter results aren't expected to set the pattern for the full year.

The company's foreign energy earnings were $676 million, up by 146 percent over the first-quarter 1979 level. A major part of the earnings gain was a $235 million increase in foreign inventory profits.

Mobil reported these earnings for its major subsidairies:

Montgomery Ward lost $46 million on a sales volume essentially unchanged from the first quarter of 1979 when it lost $4 million.

Container Corp. of America earned $21 million, an increase of $9 million.

Mobil's worldwide chemical operations earned $38 million, up 40 percent and led by gains in petrochemicals and fertilizer products.

The company's U.S. earnings averaged 4.1 cents a gallon on all products for the 12 months ended March 31, compared with 3.5 cents a gallon during calendar year 1979, the company said.

Mobil's estimated investment in exploration and production totaled $161 million in the first quarter, up 6 percent from a year ago.

Expenditures on exploration and production overseas totaled $159 million in the first quarter, 64 percent more than the year before, reflecting sharply expanded production of liquified natural gas from Indonesia, and increased North Sea oil production.