MIAMI — More than 80 years ago, Germany sold tens of thousands of bonds to American investors in an effort to recover financially from World War I. Later, Adolf Hitler used some of the money raised by those bonds to build the powerful Nazi war machine that would ravage Europe during World War II.

Now, a half-dozen U.S. bondholders are turning to federal courts in an effort to force Germany to make good on its promise to repay the debts, which today could be worth hundreds of millions, if not billions, of dollars. Action has been heating up in lawsuits filed in Miami, New York and Chicago, including a victory for investors last month when an appeals court rejected Germany's attempt to dismiss their case.

If the bondholders ultimately win, their lawyers could ask judges to seize German assets in the U.S. to repay them, a tactic that has worked in other legal disputes over money owed by foreign governments.

But if Germany prevails, the bondholders argue, it could undermine the global system through which governments raise money by issuing bonds.

"Our position is not only correct under the law, it would avoid such a potentially far-reaching precedent," said investor attorney Sam Dubbin of Coral Gables, who has frequently represented Holocaust survivors in Nazi-related claims.

Enrico Brandt, a spokesman for the German Embassy in Washington, said the lawsuits are baseless. Brandt said the only way bondholders can redeem the securities is to go through a validation process mandated by a 1953 international treaty and later enshrined in German law.

"Consequently, the efforts of the plaintiffs to outmaneuver the validation procedure by suing in the United States will fail," Brandt said.