NEW YORK (CNN/Money) - Discount chain Wal-Mart Stores Inc. Thursday reported a 3.8 percent increase in its August sales at stores open at least a year, falling short of company expectations and well below year-ago levels, as consumers tightened their wallets in an uncertain economy.

Discount chains like Wal-Mart (WMT: down $1.55 to $50.79, Research, Estimates) and rival Target Corp. (TGT: down $1.40 to $32.92, Research, Estimates) have been outperforming other types of retailers as Americans have become more bargain-savvy in the face of trying economic times, including a shaky job market.

But July became the first month in which that nervousness finally extended to the discount-chain titans, which had been feeling few effects of the down economy. Back-to-school sales have been sluggish so far, prompting many chains to offer big discounts earlier than in past years.

"We are really seeing a cautious consumer who is cutting back on discretionary spending," said Kurt Barnard, president of Barnard's Retail Consulting, who was not surprised by Wal-Mart's disappointing sales.

During the first half of 2002, Wal-Mart had regularly projected monthly sales growth of 5-to-7 percent, but then lowered that to 4-to-6 percent for August. The company reported a 7 percent increase in sales for the same period a year earlier.

The world's biggest retailer said sales at its core Wal-Mart stores rose 4.3 percent in the month, compared with a 7.2 percent jump a year earlier. Meanwhile, sales at its Sam's Club wholesale operation increased just 1.1 percent, compared with a 6.1 percent increase a year earlier.

Shares of Bentonville, Ark.-based Wal-Mart were down about 3 percent in Thursday trading.

Target, meanwhile, reported a 0.1 percent decline in its August same-store sales from a year earlier. The discount chain, known for its "cheap chic," said the number was below company expectations. This is the second consecutive month Target has missed monthly sales goals. In addition to Target discount stores, the company also owns the Mervyn's and Marshall Field's department stores.

CEO Bob Ulrich said Wall Street's third-quarter earnings forecast for a profit of 31 cents a share remains achievable, but "could be at risk by a penny or two if sales remained weaker than expected."

Kohl's Corp. (KSS: down $1.26 to $67.34, Research, Estimates), the moderately priced department-store chain, surprised Wall Street with a modest 4 percent increase in same-store sales last month. Kohl's which analysts have credited with tight management and strong margins, had regularly reported high single-digit to double-digit monthly same-store sales increases until now.

Federated Department Stores (FD: down $0.21 to $35.30, Research, Estimates), which operates Macy's, Bloomingdale's, and other popular chains, said August same-store sales tumbled 5.8 percent. However, CEO James Zimmerman said he was encouraged by stronger Labor Day weekend sales and forecast a 1-to-3 percent same-store sales increase for the fall season.

Sears, Roebuck & Co. (S: up $0.18 to $45.13, Research, Estimates) reported an 11.1 percent drop in August same-store sales. CEO Alan Lacy said the company's strategic initiatives are progressing well, with the greatest disruption to store performance occurring this month. He said the company continues to expect 2002 earnings to increase 22 percent from a year ago to $5.15 a share.

Meanwhile, department store J.C. Penney Co. (JCP: up $0.13 to $17.03, Research, Estimates) said its August same-store sales at its department stores increased 2.9 percent, led by fine jewelry and back-to-school clothing. Same-store sales at its Eckerd drug store division increased 5 percent from a year earlier. Catalog sales declined 24.7 percent.

The Plano, Texas-based company also said it remains comfortable with third-quarter earnings of 15 cents to 21 cents a share. Analysts polled by earnings tracker First Call expect a profit of 19 cents a share.

However, another department store chain, Dillard's Inc. (DDS: down $0.47 to $23.97, Research, Estimates), saw its August same-store sales slip 3 percent.

And Gap Inc., the troubled operator of Gap, Old Navy and Banana Republic reported a 2 percent decline in same-store sales, which is a marked improvement from the 17 percent decline it posted a year earlier. The company, which is in the midst of a turnaround effort following some fashion missteps, reported improved results across all divisions.

"While we experienced a slow start to August, performance improved in the second half of the month as we stepped up strategic promotional activity and implemented fall marketing," Chief Financial Officer Heidi Kunz said in a statement. "Despite the increase in promotions, total company merchandise margins improved year over year and met beginning-of-month projections."

Shares of San Francisco-based Gap (GPS: up $0.76 to $12.66, Research, Estimates) were up 7 percent in Thursday trading.

Other retailers reported mixed August sales results Thursday.

Home furnishings retailer Pier 1 Imports Inc. (PIR: up $0.85 to $19.07, Research, Estimates) posted an 8.6 percent increase in August same-store sales and a 5.8 percent increase in second-quarter same-store sales. The company raised second-quarter earnings guidance to 23 cents a share from last month's revised 20 cents to 21 cents a share. Analysts polled by earnings tracker First Call anticipate a profit of 21 cents a share.

Men's Wearhouse (MW: down $0.99 to $18.46, Research, Estimates) said August same-store sales at U.S. stores declined 12.7 percent from a year earlier; Jos. A Bank Clothiers Inc. (JOSB: up $0.01 to $18.76, Research, Estimates), another men's apparel retailer, reported a 14.6 percent jump in August same-store sales; Limited Brands (LTD: down $0.17 to $14.99, Research, Estimates), which operates Limited, Victoria's Secret, Bath & Body Works and other chains, reported a 1 percent increase in August same-store sales; Cato Corp. (CTR: down $0.24 to $18.76, Research, Estimates), a women's apparel chain, reported a 3 percent same-store sales decline for last month, slightly below company expectations; and Gottschalks Inc. (GOT: down $0.06 to $2.20, Research, Estimates) reported a 1.7 percent drop in same-store sales.