The monthly barrage of same-store sales data from U.S. retail chains will hit Wall Street Thursday morning, and investors are prepared to scrutinize the results for any signs of weakness in consumer spending that could threaten economic growth.

Research firm RetailMetrics expects its overall index tracking same-store sales from more than 70 major chains to increase 3.7% in July from a year earlier. That comes on top of last year's 3.7% jump, and would demonstrate that cash registers are still ringing across the country, even while investors fret about rising interest rates, soaring energy prices and a softening housing market.

"Consumers are still facing all these headwinds, but as long as the job market holds up here, we think they're going to meet expectations, or maybe slightly exceed expectations," says Ken Perkins, president of RetailMetrics.

Same-store sales, or comps, measure sales at stores that have been open for at least a year. Factoring out sales growth related to new store openings, the metric provides what analysts view as a snapshot of a company's competitive strength.

Wal-Mart

(WMT) - Get Report

provided an early show of resilience. Over the weekend, the world's largest retailer reported a 2.4% same-store sales gain for July, hitting the high end of its forecast and rebounding from weak results in June.

Wal-Mart's sales were particularly encouraging, because its low-income customer base is viewed as being vulnerable to the spending strains posed by gas prices. That said, the company could be attracting higher-end customers into its stores with low prices as shoppers look to save money.

Despite its massive size and scope, Wal-Mart hasn't always proved to be an accurate predictor of the retail industry as a whole. But Perkins says analysts are expecting the discounters, including Wal-Mart's direct competitors like

Target

(TGT) - Get Report

and

Costco

(COST) - Get Report

, to post an overall gain of 3.2%. For its part, Target warned in mid-July that same-store sales would likely be up 3% to 4%, down from its previous forecast of 4% to 6%.

Strength from drugstore chains should carry the sector, as evidenced by the 9.7% comps already posted by

Walgreen

(WAG)

for the month. Elsewhere, specialty chains are expected to show some weakness, with analysts expecting an overall gain of just 2.2%. Wall Street's beloved teen-apparel retailers should fare better, and are expected to show a 4.9% increase.

"July started out relatively well, but as the month moved on, we got a transition with summer clearance goods being moved out of stores and back-to-school and fall stuff hitting the shelves," says Perkins. "That, coupled with some increased temperatures towards the back of the month, didn't help."

While July results should hold up, the outlook for consumer discretionary spending going into the back half of 2006 remains tenuous. Expectations for a spending slowdown have wrought selloffs in the stock market, as evidenced by the 8.4% decline in the S&P Retail Index so far this year. Most of that decline comes from selling in the last three months as the long-held view that consumers could not continue to spend so lavishly gained acceptance.

"Valuations have definitely come down in the retail sector," says Perkins. "It's not very attractive, because the long-term prognosis is that the rest of this year is going to be tough on retailers. They're going to have to execute better than they have in the last several years going into the holiday shopping season. Inventory levels seem to be pretty lean, which is good, but they're going to have to get fashions and products just right."

In this environment, investors will be straining to hear any commentary from retailers about the strength of back-to-school spending in early August.

"August is really going to be a key month, because it's the big back-to-school month, and back-to-school shopping is usually a good harbinger of how the holiday season will fare," says Perkins. "There's going to be a big focus on August."