CHICAGO (MarketWatch) – McDonald’s Corp., which long had seemed protected against global economic turmoil, showed some cracks in its armor Monday, reporting a rare dip in quarterly profit that also came up shy of Wall Street’s expectations.

Before the start of trading, McDonald’s MCD, -1.03% said that it earned $1.35 billion, or $1.32 a share, for the period, down from $1.41 billion or $1.35 a share in the same quarter a year ago. Revenue was essentially flat at $6.92 billion. That compares with the average estimates of analysts polled by FactSet for the fast-food chain to earn a profit of $1.38 a share on sales of $6.94 billion.

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Globally, the company’s same-store sales were up 3.7% and held positive in every geographic region.

One of the main culprits was the stronger U.S. dollar, which siphoned off 7 cents a share from its bottom line. But Chief Executive Don Thompson also noted McDonald’s is being hurt by “the slowing global economy and persistent economic headwinds,” as well as by investment in operations.

However, he added, “while the environment has become more challenging, we continue to see significant opportunities to further differentiate and grow the McDonald’s brand.”

Until now, perhaps, McDonald’s has survived, even thrived, during tough times as diners sought less-expensive fare. The company also has had great success with numerous new products, while extended hours at many locations have lengthened the business day. In addition, the slowdown has had another benefit of keeping labor costs down.

Currency is apt to be a continuing problem as the euro seems unlikely to bounce back strongly anytime soon. What’s more, drought is driving up some commodity prices around the world; that could begin to bite.

The earnings news sent shares of McDonald’s down almost 5% at one point during Monday trading. Losses later eased off to around 3% at $88.84.

Mark Kalinowski of Janney is keeping his buy rating on the stock because of “impressive same-store sales trends in the U.S., which we believe are attributable to best-in-class store-level execution” and a belief that “McDonald’s will continue to grab additional market share in all three major geographies, helping the stock gradually over time.”

But based on the second-quarter profit shortfall, he cut his 2012 earnings estimate by 19 cents, to $5.45 a share and his 2013 estimate by 20 cents, to $6 a share.

Kalinowski also noted that at least some of the relatively bad news was already expected.

“Keep in mind that as far back as several months ago, McDonald’s was highlighting some extra anticipated costs in the second quarter for an owner/operator [franchisee] convention, in the second and third quarters for the London-based summer Olympics, and throughout the year for technology-related initiatives.”

Jim Yin at Standard & Poor’s maintained a strong-buy rating on the stock although he cut his price target by $3 to $104 and trimmed his profit forecast.

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“In addition to slower growth in all geographical regions, results were hurt by unfavorable foreign-currency exchange and higher commodity and labor costs,” he wrote. “We project lower operating margins on increased marketing expenses and capital expenditure, as the company tries to retain its customers.”

Finally, Yin pointed out, “we believe [the company] will fare better than most of its competitors during difficult times because of its value appeal.”