NEW YORK — Greek debt has been tempest-tossed in recent weeks, but investors in U.S. regional bank stocks could be excused for reaching for Dramamine themselves.

A whole slew of American regional lenders, like Fifth Third Bancorp, Huntington Bancshares Inc. and Regions Financial Corp., have no clear interest in the sovereign debt of Greece. But that lack of connection hasn't stopped investors from buying and selling regional-bank stocks in tandem with recent broader market rallies and sell-offs, many tied to fears of Greece.

"You've got the fourth-order effect going on here," said Jaime Peters, analyst at Morningstar Inc. "It's an issue."

In keeping with recent tradition, regional shares soared Monday after European leaders announced a new plan to back-stop both Greece's debt and the viability of the euro. The KBW Regional Banking Index rose 4.1%, boosted in part by sharp rallies of some once-distressed regional-bank stocks. Fifth Third was recently up 7% to $14.25, while Huntington was up 5.3% to $6.39.

Just last week, some investors worried that a European meltdown could send ripples far enough through the world's economy that they'd eventually swamp the regional banks' tepid signs of recovery. The KBW Regional Banking Index fell about 9% last week.

The typical American regional bank carries little, if any, cross-border exposure. Whereas Wall Street banks might hold sovereign debt, help foreign governments manage their finances, or lend to European banks heavily exposed to weaker sovereign credits, U.S. regional banks largely collect deposits and lend money to domestic companies. Whoever a regional bank lends money to, investors can be reasonably sure most of its borrowers are located within the nation's confines.

Yet the lenders' relatively simple business model hasn't translated into smooth sailing through the financial crisis. Regional banks placed big bets on commercial real estate during the housing boom, and their stocks have been volatile as investors have scurried to decide whether their worst loan problems have passed.

To be sure, if the European sovereign-debt crisis dragged the world into a double-dip recession, U.S. banks would ultimately feel pain as well.

In fact, some analysts have blamed regional bank stocks' recent large price swings on investors rushing to place or cover short positions. A number of the sector's stocks have more than doubled compared to their 52-week lows, enticing some investors to bet their rally will soon fall to earth.

"They are available to short," said Christopher Whalen, managing director of Institutional Risk Analytics, a research and risk-management firm. I "don't think there is any real correlation" to Greece.

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