Marriott Corp., anticipating unpaid airline catering bills left by Braniff International, stashed away $3 million in reserves to cover the expected loss, cutting its profit gains in its second quarter from 10 percent to 3 percent.

The Bethesda-based international food and lodging company had second-quarter earnings of $22.4 million (82 cents a share) compared with $21.8 million (81 cents) last year.

Although profits were flat, the company's sales were up sharply over last year's, jumping from $463.6 million to $600.9 million. Marriott's recent acquisition of Host International, an airport food business, contributed about $70 million in new sales for the second quarter, the company reported.

Braniff International owed Marriott $5.7 million for airline catering services when it sought reorganization under Chapter 11 of the federal bankruptcy laws. Marriott has set aside $3 million in reserves to cover its expected loss when Braniff's assets are ultimately divided among its creditors.

Marriott's profit picture would be slightly brighter if it had not suffered the Braniff loss, company officials said yesterday. Net income for the second quarter would have risen 10 percent instead of 3 percent and earnings would have been 88 cents per share.

For the first half of 1982, Marriott reported net income of $39.3 million, an increase of 9 percent over $36.2 million for the 1981 first half. Earnings per share were $1.44, up 7 percent from $1.35 a year ago.

Chesapeake Corp. of Virginia, the West Point-based manufacturer of paper, pulp and lumber products, suffered from a weak market for lumber products and reported a steep decline in profits for the second quarter.

Net income dropped from $7.1 million ($1.15) in the second three months of last year to $1.8 million (23 cents) for the same period this year. Sales also dropped, from $69.7 million to $56.7 million.

Sales and profits also declined substantially comparing the first 24 weeks of 1981 with the same period this year. Profits fell to $3.7 million (59 cents) from $13.0 million ($2.11). Sales were $116.3 million for the beginning 24 weeks this year; $133.5 million last year.

Company officials said a decline in demand for mill products, corrugated containers, plywood and manufactured housing products accounted for about 70 percent of the reduction in sales. Continuing price drops for lumber products were responsible for the remaining decrease in dollar sales, officials said.

"Current selling prices for most of the company's mill products are below January 1981 levels and consequently our margins have been severely squeezed," said J. Carter Fox, president.

The O'Sullivan Corp., a Winchester, Va.-based maker of rubber, plastics products and general warehouser, reported a small increase in second-quarter profits over last year on a small drop in sales.

Second-quarter profits before taxes were $3.0 million (54 cents) compared with $2.8 million (48 cents) for the same period last year. Sales were down from $20.5 million to $19.1 million.

The first-quarter sales and profit pattern for O'Sullivan was repeated in the first six months of 1982. Net sales were down from $37.2 million last year to $35.1 million this year, while profits rose from $5.0 million to $5.3 million.