Presidents Dmitri A. Medvedev of Russia, left, and Hugo Chavez of Venezuela plan joint naval exercises.

By SIMON ROMERO, MICHAEL SLACKMAN and CLIFFORD J. LEVY
CARACAS, Venezuela

AS THE PRICE of oil roared to ever higher levels in recent years, the leaders of Venezuela, Iran and Russia muscled their way onto the world stage, using checkbook diplomacy and, on occasion, intimidation.
Now, plummeting oil prices are raising questions about whether the countries can sustain their spending - and their bids to challenge United States hegemony. For all three nations, oil money was a means to an ideological end.
President Hugo Chavez of Venezuela used it to jump-start a socialist-inspired revolution in his country and to back a cadre of like-minded leaders in Latin America intent on eroding Washington’s once-dominant influence.
Iran extended its influence across the Middle East, promoted itself as the leader of the Islamic world and used its petrodollars to help defy the West’s efforts to block its nuclear program.
Russia, which had suffered a humiliating economic collapse after the fall of communism, began rebuilding its military, wrested control of oil and gas pipelines and pushed back against Western encroachment in the former Soviet empire.
But such ambitions are harder to finance when oil is around $70 a barrel, than when it is at $147, its price as recently as three months ago.
Russia, Iran and Venezuela have all based their spending on oil prices they thought were conservative but are now close to the market level. Significant further drops could tip the three countries into deficit spending or at least force them to choose among priorities.
Venezuela’s Surge in Spending
Mr. Chavez was emphatic in September when he announced that Venezuela would engage in joint exercises with the Russian Navy in the Caribbean, made possible in part by a flood of petrodollars used to buy Russian weaponry. “Go ahead and squeal, Yanquis,” he said. “Russia’s naval fleet is welcome here.”
Domestic spending in Venezuela has surged, through the creation of social welfare programs that furthered Mr. Chavez’s goal of building a socialist-inspired state. The 2009 budget, based on $60-a-barrel oil, includes a 23 percent increase in government spending, to $78.9 billion.
At $140 a barrel for oil, that was conservative. With prices now uncomfortably close to $60 a barrel, economists in Venezuela are expressing alarm over the government’s ability to pay its bills, including those for arms. Venezuelans are already struggling with an inflation rate of 36 percent, one of the highest in the world.
“This country will be paralyzed because it is so dependent on petroleum,” said Oscar Garcia Mendoza, president of Banco Venezolano de Credito, a private bank.
The Power of Iranian Reserves When President Mahmoud Ahmadinejad of Iran presented his budget to Parliament in 2007, the United Nations Security Council had already imposed economic sanctions on Iran because of its nuclear program. The president said it did not matter. “Even if they issue 10 more such resolutions,” he said, “it will not affect Iran’s economy and politics.” He was partly right. It hardly affected Iran’s politics.
One of the main reasons it was able to endure the economic punishment was the price of oil. Iran has the second largest known oil reserves in the world, and it has used them in recent years as a political and economic weapon to defy the West while promoting its own agenda.
At home, oil money allowed Iran’s ideological hard-liners to preserve their monopoly on power, to buy political allegiances and to offset the fiscal damage of their economic policies. All that may now have to be recalibrated.
“The drop in oil prices will make the Iranian regime re-examine its calculations because its political immunity is less,” said Mustafa El-Labbad, director of the East Center for Regional and Strategic Studies, an independent research center in Cairo. “Their regional presence and role will shrink.” Russia’s Energy Dominance On a winter day in 2006, Russia suddenly cut off the supply of natural gas to Ukraine, where a pro- Western government had come to power.
The Kremlin cited a dispute over prices. But some Western officials said Vladimir V. Putin, Russia’s president at the time and still its paramount leader, was sending a message: Russia was willing to use its vast energy reserves to try to reassert the dominance it lost with the Soviet Union’s collapse.
Two months ago, the muted reaction of some European nations to Russia’s invasion of Georgia seemed to indicate that Mr. Putin’s policy was working, some foreign policy analysts said. Europe had become dependent on Russia’s gas and could not afford to mount a strong challenge, they said.
Now, however, with gas prices tumbling, this strategy has been thrown into question. Europeans may no longer be as intimidated .
“The more other countries are nervous about their energy security, the better Russia is geopolitically,” said Peter Halloran, chief executive of Pharos Financial Group, an investment fund based in Moscow.
Still, he and other experts said Russia was better positioned to weather lower prices than were many other oil and gas producers, because it had adopted conservative fiscal practices in recent years.
Opposition politicians in Russia said they did not perceive sagging prices as undermining Mr. Putin’s power. “I think that it’s too early,” said Grigory A. Yavlinsky, an opposition leader. “The crisis at the moment is not related to the population enough. The banks are still open, and unemployment is not yet going higher. It’s a threat, but it’s only a potential threat.”