Marriott Corp. reported earnings per share of 50 cents for its 1988 third quarter ended Sept. 9, an increase of 19 percent from 42 cents a year ago.

Net income for the 1988 third quarter was $58.20 million, compared to $56.70 million for the same period last year. The company said net income increased only three percent over the 1987 quarter primarily because of higher interest expense associated with the company's share repurchase program.Sales totaled $1.67 billion, a gain of 12 percent from $1.49 billion in the 1987 third quarter.

J.W. Marriott, Jr., chairman and president, said operating income was up 12 percent in the 1988 third quarter. He said the company had higher profits in each of its three major lines of business - lodging, contract services and restaurants - and continues to expect solid gains for the balance of the year.

For the 1988 nine months, Marriott reported earnings per share of $1.39, up 17 percent from last year.