The nation's retailers yesterday reported stagnant July sales, as consumer spending stalled in face of rising personal debt and higher delinquency rates on credit payments.

Chicago-based Sears, Roebuck & Co., the largest U.S. retailer and the bellwether for the industry, announced its sales for the four weeks ended Aug. 3 dropped 0.3 percent to $1.71 billion from $1.72 billion in the same period last year.

Sears Chairman Edward R. Telling blamed the sales slowdown on "continuing softness in the economy and highly competitive conditions in the general merchandise industry."

K mart, the No. 2 retailer, with headquarters in Troy, Mich., posted a modest 4.5 percent sales gain in July, to $1.52 billion from $1.45 billion in the same month last year.

K mart Chairman Bernard Fauber said lower-than-planned sales continue to reflect the lackluster pace experienced in June, and along with competitive pressures have made it impossible for the company to match its record 1984 second-quarter profits.

Third-ranked J. C. Penney Co. of New York said its July store and catalogue sales declined 0.6 percent to $803 million from $808 million in the year-earlier period.

Monroe H. Greenstein, retail analyst at Bear Stearns & Co. in New York, said July sales were even more sluggish than indicated by the reports because a calendar change gave some stores an extra day in the latest period.

"Consumers are more cautiously buying general merchandise," perpetuating a trend that has dogged the industry since April, he said.

This prudence reflects higher consumer debt, a rising delinquency rate in credit payments and a tendency to make smaller payments, Greenstein said.

Analysts predicted retail sales would rebound somewhat in August with the opening of the back-to-school buying season.

They also said sales this month would benefit from comparisons with results last August, when sales weakened.

K mart's Fauber said the arrival of fall fashions and improved consumer confidence levels "indicate that an increase in sales will be experienced in the important latter half of 1985."

Jeffrey Edelman, a retail analyst with the investment firm Dean Witter Reynolds Inc. of New York, said the weakness in July sales was evident nationwide and across product lines.

Jeffrey Feiner, an analyst with Merrill Lynch, Pierce Fenner & Smith Inc., pointed out that some department stores did better than the mass merchandising and discount-store chains.

"This reflects the ability of the department stores' customer base: i.e., a somewhat more affluent customer, to withstand sluggish economic conditions," Feiner said.

For example, Federated Department Stores Inc., whose operations include such chains as Bloomingdale's, Abraham and Strauss and Burdine's, had a July sales gain of 8.4 percent.

Sales rose 21.2 percent at No. 5 Dayton Hudson Corp., which also operates a variety of chains from its headquarters in Minneapolis.

"The retail environment remains difficult and sales in the general merchandising division continued below expectations," said Federated Chairman Howard Goldfeder.

Among other retailers, sixth-ranked Montgomery Ward & Co., a unit of Mobil Corp. based in Chicago, reported its sales declined 5 percent to $318.4 million from $335.2 million a year earlier.

The July results did not include Ward's catalogue business, which is being discontinued, or its Jefferson Ward stores, which are being sold.

F. W. Woolworth of New York said its July domestic sales increased 5.3 percent to $235.6 million from $223.8 million a year earlier.

Wal-Mart Stores Inc., based in Bentonville, Ark., posted a 35 percent jump in July sales to $640 million from $475 million the year before on the addition of 120 new stores. Sales on a comparable-store basis were up 12 percent.

New York-based Associated Dry Goods, parent of Lord & Taylor and Caldor, had an 11.7 percent July sales gain to $249.3 million, from $223.2 million a year ago.

Carter Hawley Hales Stores Inc. of Los Angeles reported its sales were up 12.7 percent to $249.5 million from $221.4 million last July.

Allied Stores Inc., the New York-based parent of Brooks Brothers and Jordan Marsh, announced its sales advanced 6.7 percent to $234.3 million from $219.5 million in July 1984.

Zayre Corp., based in Framingham, Mass., recorded a 17.9 percent sales increase in July to $238.8 million from $202.6 million