Kay Jewelers Inc., still affected by interest expenses incurred in its acquisition of J.B. Robinson Jewelers last year, reported a loss of $353,000, or 4 cents a share, for its third quarter, down from the $111,000 profit (1 cent a share) posted in the same time period a year ago.

Despite the loss, the Alexandria specialty retailer said it expects to fare much better next quarter, making 1987 more profitable than last year, when the company earned $9.7 million. Typically, almost all of Kay's profits come during the fourth-quarter Christmas season.

Revenue for the latest quarter was $78.1 million, up 42 percent from $54.8 million last year. However, much of that gain was due to the acquisition of the 94 Robinson stores, whose sales figures were not included in Kay's sales last year. Kay bought the stores last December.

For the first nine months of this year, Kay lost $4.3 million (54 cents), more than five times the $664,000 (9 cents) loss incurred a year ago.

Revenue for the nine months was $210.7 million, up 39 percent from the $150.5 million of a year ago. The gains also were largely due to the Robinson acquisitions.

Washington Gas Light Co. said it suffered its normal seasonal loss in the third quarter, a period when fewer residential heating customers are using natural gas.

The natural gas distribution company posted a loss of $10.9 million (65 cents) in the third quarter, compared with a loss of $7.4 million (45 cents) for the same quarter of 1986. Revenue for the quarter was $74.2 million, down 3 percent from $77 million last year.

A WGL spokesman said the company always experiences a loss in the third quarter, but makes up for it in the other quarters.

For the first nine months of the year, the company's profits fell 10 percent, to $18.1 million ($1.08), from $20.1 million ($1.22) for the nine months last year. Revenue declined 6 percent, to $486 million, from $515.1 million.