Smithfield Foods Inc., of Arlington, reported a first-quarter profit of $638,000 (24 cents a share) for the 13 weeks ended July 28, compared with a loss of $732,000 (19 cents) in the same period of last year.

Quarterly sales increased to $188.6 million from $131.4 million last year.

The pork-packing and processing company attributed much of its improved performance to continued gains by its subsidiary, Gwaltney of Smithfield Ltd., which it acquired in 1981. Smithfield said it was "delighted" with the results. The company said it "generally loses money" in the summer quarter because of seasonally higher hog prices and slower sales.

*Bresler & Reiner Inc. reported a 29 percent drop in second-quarter net income to $457,000 (41 cents) for the three months ended June 30 from earnings of $640,000 (58 cents) in the same quarter of 1984.

The District-based company said quarterly revenue decreased to $3.2 million this year from $3.3 million last year.

For the six months ended June 30, earnings declined 49 percent to $862,000 (78 cents) from $1.7 million ($1.54), while revenue slid to $6.4 million from $8 million in the first half of last year.

Chairman Charles S. Bresler said "the lower revenue in 1985 reflects a substantially lower volume of home sales, primarily because the company has not had available sufficient finished building lots." The company sells homes and operates a motel, apartment projects and a shopping mall/office complex.

*Allegheny Beverage Corp. reported first-quarter profits of $59.9 million ($9.39), up 2,895 percent, compared with earnings of $2 million (32 cents) in the same quarter of last year. The results include a one-time, after-tax gain of $68.2 million ($10.68) from the sale of Allegheny's soft drink bottling subsidiary.

First-quarter revenue increased to $225.3 million from $119.3 million.

The company, based in Cheverly, Md., sold the bottling subsidiary in May and recently completed its $225 million acquisition of Servomation Corp., a food service and vending company. Allegheny said it plans to merge its Macke food service business with Servomation's to form a new entity, Service America Corp. Allegheny's other operations include building maintenance, laundry services and office furniture retailing.

*James River Corp. reported a 6 percent increase in first-quarter profits to $23.7 million (68 cents) from earnings of $22.4 million (65 cents) in the same period last year.

The Richmond-based company said sales for the period ended July 28 increased to $629.9 million this year from $625.2 million in the comparable 1984 period.

James River processes wood, wood pulp, synthetic fibers and plastic resins into a variety of products, including paper towels, tissues, cartons and other paper products.