C3 Inc., a Reston firm that installs custom designed minicomputer and microcomputer products and systems, reported record earnings for its fiscal year ended March 31 of $8.9 million ($1.05 a share), up 6.4 percent from $8.4 million (98 cents) in the previous year. Revenue was $62.5 million, up 28.8 percent from the previous year's $48.6 million.

Fourth-quarter net income was $3.6 million (42 cents), an increase of nearly 50 percent over the $2.4 million (28 cents) earned in the final quarter of the previous year. Revenue was $22.8 million compared with $13.5 million.

C3 said that renewed buying under existing contracts with the U.S. government--particularly the Coast Guard--accounted for the increases.

Suburban Bancorp reported earnings for the first quarter of $4.853 million ($1.02 a share), a 6.7 percent increase over $4.550 million (96 cents) for the same quarter a year ago.

Return on stock holders' equity was 14.67 percent, and return on assets was 0.96 percent.

Officials said that the first-quarter gain was primarily due to a $1.8 million increase in operating income, about half of which was generated by fees charged on high-rate money market deposit accounts and for corporate cash-management services. About 30 percent of the increase reflected funds from credit card fees.

Fair Lanes Inc. of Baltimore, an operator of bowling centers, reported earnings of $2.847 million (42 cents a share) for its third quarter ended March 31, up from $2.462 million (36 cents) for the same quarter a year before. Revenue was $22.076 million, up from $2.462 million.

Nine-month earnings were $5.178 million (77 cents) on revenue of $58.577 million compared with earnings of $4.3 million (63 cents) on revenue of $55.611 million a year earlier.

The company said that discontinued operations included a gain of $287,000 (4 cents) on the sale of five Treadway Inns.

Virginia Electric and Power Co. reported net income for the 12 months ended April 30 of $279.168 ($1.92 a share) compared with $258.157 million ($1.92) for the 12 months ended April 30, 1982. The company's revenue was $2.415 million, compared with $2.238 million for the 12 months ended April 30, 1982.

Net income for the month of April was $13.171 million (70 cents) compared with $10.924 million in April 1982. Revenue for the month was $190.362 million compared with $165.690 million for the same month a year before.

Trading in Dominion Resources (stock symbol DomRs) common stock began for the first time yesterday on the New York Stock exchange. The new entity is the result of restructuring by Vepco to form a holding company of which Vepco is now a wholly owned subsidiary.