The rules that govern fiscal policy in the eurozone should be simplified to ensure that member governments cut their debts, economists at the International Monetary Fund said in a paper published Friday.

The rules, enshrined in the 1997 Stability and Growth Pact, are intended to ensure that national governments don't take advantage of their membership of the eurozone to borrow excessively, and thereby threaten the stability of the currency area.

But the rules have been regularly flouted since the euro was launched in 1999 and failed to prevent surges in borrowing that contributed to the currency area's debt crisis, which began in 2010 and continues to this day as Greece seeks an agreement with the rest of the eurozone and the IMF that would enable it to repay its debts.

A number of reforms to the rule book have followed in the years since the crisis, increasing its complexity without securing full compliance, the most recent changes coming earlier this year.

In the paper published by the IMF, seven of its economists said the very complexity has made it difficult to ensure governments pursue fiscal policies that will reduce their debt levels over the medium term.

The combined debts of the eurozone's member governments rose again in 2014, reaching 91.9% of gross domestic product, compared with an upper limit under the budget rules of 60%.

"Compliance remains weak," the economists wrote. "This reflects the complexity of the framework, which has resulted in both unintended violations and the exploitation of loopholes, and has gone hand-in-hand with weak enforcement."

The IMF economists also said the long-standing requirements that budget deficits don't exceed 3% of gross domestic product and that government debt should fall toward 60% of GDP are no longer consistent with each other.

The damage inflicted by the financial and debt crises mean the eurozone's growth potential is much lower than it was when the rules were set down, so even deficits as low as 3% of GDP won't deliver the desired reduction in debt ratios. In fact, debts will probably rise if deficits aren't lower.

"This implies a 100% of GDP debt level over the medium-term, resulting in an inconsistency between the existing debt and deficit targets; in other words, the action path implied by the deficit target diverges from that required by the debt target," the economists wrote.

The IMF economists considered a range of alternative, simpler rules for fiscal policy, and concluded the best option would be a limit on the growth of government spending calibrated to bring down government debt as a share of economic output.

"Expenditure rules are more directly related to the formulation of the annual budget, which sets legally binding spending appropriations, thereby providing clear operational guidance to policy makers," they wrote. "Second, expenditure rules are less complex and therefore easier to communicate and monitor."

The IMF economists accept that the proposed reforms will take time to implement, since they would likely face legal challenges and may even require changes in the European Union's treaties.

But they said the effort would be worth it if it helps ensure the eurozone can continue to exist.

"Working for a simpler and more robust fiscal framework may be the best response to recent skepticism about the European project," they wrote.

The IMF noted that while it published the paper, the analysis presented within it isn't its official policy.

Write to Paul Hannon at paul.hannon@wsj.com

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