MOSCOW — A steep decline in oil prices is straining the budgets of major petroleum-exporting countries around the globe, raising a specter of spending cuts in Russia, where the economy is under pressure from Western sanctions, and posing a potentially grave security challenge for Iraq, which is already struggling to finance its fight against the Islamic State.

From Moscow to Caracas, Riyadh to Baghdad, in Tehran, Algiers, Kuwait City and Lagos, political leaders, finance ministers and central bankers have been scrambling to confront the plunge in prices — roughly 25 percent since a peak in June — driven by increased production in the United States and by projections of sustained cuts in demand in many developed countries, as well as decelerating growth in China.

The price drop is mostly welcome news in the developed world, and particularly in Washington. Countries like Russia, Iran and Venezuela that in recent years have sought to thwart America’s influence could begin to moderate their behavior, as they come under growing financial pressure.

While Russia maintains reserves of hundreds of billions of dollars as a cushion for precisely this sort of price drop, there are already signs of tensions here.