Marriott Corp. yesterday reported its most profitable guarter ever, as earnings jumped 46 percent to $18.6 million from $12.8 million for the 12 weeks ended Oct. 20.

Saying, "business continues brisk for us," President J.W. Marriott Jr. said the biggest gains came in the hotels and contract food operations, with hotel profits up 22 percent on a 25 percent sales gain and food service earnings up 27 percent on a 13 percent gain.

Total sales for the Bethesda company were up 15 percent from a year earlier, to $316 million from $275 million.

Per share earnings increased to 49 cents from 34 cents, figured on either a primary or fully diluted, basis. Based on a weighted average of shares outstandings, earnings were 51 cents against 35 cents, the company said.

Marriott's president said the 22 percent gain in hotel earnings means lodging now represents almost half of the company's total operating profit. Occupancy rates and room rates are both up, and by selling five hotels to a major insurance company. Marriott trimmed its interest expense by the equivalent of 3 cents per share.

Earnings from catering for U.S. airlines were off, Marriott said, but the contract food division made up for them with growth in international inflite business and airport and highway rest stop operations. Restaurant sales were up 12 percent and profits up 11 percent, with the Roy Rogers, Hot Shoppes, Big Boy and Farrells divisions showing gains.

Because the company is switching its fiscal year Marriott also reported results for the 12 months ended in October. Earnings were $51.9 million ($1.42 per share) up from $38.3 million ($1.05). Sales for that period increased 14.5 percent, to $1.2 billion from just over $1 billion.

Equitable General Corp. of McLean reported earnings declined to $2.1 million (75 cents per share) from $2.6 million (82 cents per share) for the three months ended Sept. 30.

"The unusual legal and consultant fees associated with merger" of Equitable General and Gulf United Corp. depressed earnings, said Equitable General President Charles E. Phillips. Shareholders will vote on the merger in December, Phillips said yesterday.

Total income for the quarter increased to $13 million from $11.9 million.

For the first nine months of its fiscal year, Equitable General's life insurance sales reached a record high of $10 million, up 5.2 percent over the same period in 1977.

Total income for the nine months was up also, to $38.5 million from $36.2 million, but earnings declined to $7.3 million ($2.43 per share) from $7.8 million ($2.43).