LONDON — As America wages a very public battle against Iran’s quest for nuclear power, Washington quietly is gaining ground on another energy front: the oil fields that are the Islamic Republic’s lifeblood.

Iran’s oil industry has raked in record amounts of cash during three years of high oil prices. But a new American campaign to dry up financing for oil and natural gas development poses a threat to the republic’s ability to continue exporting oil over the next two decades, many analysts say.

The campaign comes at a moment of unique vulnerability for Iran’s oil industry, which also faces challenges from rising domestic energy consumption, international isolation, a populist spending spree by President Ahmadinejad and trouble closing contracts with foreign oil companies — a recipe for potential disaster in a nation with one of the world’s largest reservoirs of oil.

“If the government does not control the consumption of oil products in Iran, … and at the same time, if the projects for increasing the capacity of the oil and protection of the oil wells will not happen, within 10 years, there will not be any oil for export,” Iran’s deputy oil minister for international affairs, Muhammad Hadi Nejad-Hoseinian, said in a telephone interview.

If Iran were suddenly to stop exporting its 2.4 million barrels of oil a day, such as in the event of a military strike, world oil prices probably would skyrocket. But a gradual decline probably could be offset by other OPEC members, analysts say, particularly as Iraq increases its oil production and Saudi Arabia carries out plans for significant increases in its production capacity.

The efforts by America and its allies over the past few months to persuade international banks and oil companies to pull out of Iran threaten dozens of oil and gas projects, including plans for development of Iran’s two massive new oil fields that stand to expand oil output by 800,000 barrels a day over the next four years.

“Many European banks, which had accepted financing some oil industries projects, have recently canceled them,” Mr. Nejad-Hoseinian said.

In addition, banks are no longer granting letters of credit for delivery of some supplies, ministry officials say. And as nations such as Japan begin to back out of Iran oil development under American pressure, the government in Tehran is being forced to dig deeply into its own reserve funds to get crucial new projects off the ground.

But Mr. Nejad-Hoseinian said Iran has recognized the gravity of the threat and has launched steps to head it off, including new “smart” rationing cards scheduled for distribution in March to check skyrocketing sales of cheap gasoline and an overhaul of Iran’s historically stingy contract terms in an attempt to lure big oil companies into skirting the American roadblocks.

Iran also is hoping to turn to China and Russia for help. But American officials have warned they will seek to hold China accountable under Washington’s unilateral sanctions laws if it proceeds with a $16 billion project to develop Iran’s North Pars gas field. China also has signed a memorandum of understanding under which it may take on development of the Yadavaran field in southwest Iran, expected to boost production by 300,000 barrels a day.

Iran’s oil and natural-gas dilemma has no direct connection to the sanctions adopted by the U.N. Security Council last month, which are tightly targeted at assistance to Iran’s nuclear program. Although Tehran insists it has strictly peaceful intentions, the governments of America and other countries believe the program is linked to development of nuclear weapons.

Rather, the looming crisis stems from a series of domestic problems that have converged at a time when Iran is susceptible to American attempts to capitalize on them to coerce Iran’s compliance on the nuclear issue.

Most important is the condition of Iran’s aging oil fields, which have not recovered fully from damage inflicted during the Iran-Iraq war of the 1980s. To maintain enough pressure to keep them pumping at all, Iran must divert large amounts of natural gas that might otherwise be sold.