The price of crude oil and growing tensions with Iran are bubbling to the top of economists’ and policymakers’ worry lists for 2012, as U.S. and European Union sanctions threaten to reduce the sales of Iranian oil and put pressure on one of the world’s largest petroleum exporters.

“It’s been in the background for quite some time,” said Edward Yardeni, a leading investment strategist. “I’ve characterized it as one of the four horsemen of the apocalypse for 2012. Now it’s come from behind to be at the head of the pack.”

The push for tighter sanctions on Iranian oil exports comes at a time when oil prices are already high. Last year was a record-shattering year for oil prices, which averaged $107 a barrel, about 14 percent more than in the previous record year of 2008, according to figures from the Organization of Petroleum Exporting Countries.

The U.S. oil import bill — for crude and refined products — jumped about $125 billion from 2010 to 2011.

Rising oil prices could hurt the fragile global economy, which includes economists’ other big worry: Europe.

Barclays Capital analysts noted on Friday that in terms of the euro currency, oil prices “have now almost matched their previous peak of July 2008,” draining money from economies already struggling with the sovereign debt crisis. Three of Europe’s most troubled economies — Greece, Spain and Italy — are also the E.U.’s biggest importers of Iranian crude and would be most affected by a new ban. (The United States already bars imports of Iranian crude oil.)

“At current prices, the world economy is going to grow at 3 percent to 3.5 percent this year,” said Adam Sieminski, chief energy economist at Deutsche Bank. “That’s not great, but okay. At $125 a barrel, it is only going to grow 2.5 percent, and that’s not very good. And at $150, we might only grow 1 percent, and that’s a disaster.”

Many analysts do not think Iran would risk military conflict by carrying out its threat to close the Strait of Hormuz, used by tankers carrying 17 million barrels of oil a day, about a fifth of the world’s consumption. E.U. leaders meet Jan. 23 to decide whether to embargo Iranian crude, but oil prices fell Friday on reports that any import ban would be phased in or delayed six months.

Within that time, a new overland pipeline from the United Arab Emirates would open and Libyan output, damaged by civil war, would probably return to normal. And European refiners, who buy about 600,000 barrels of Iranian oil daily, could line up new suppliers.

Moreover, that delay would give Iran yet another chance to negotiate international inspections of its nuclear program. “That’s the end game,” said Julian Lee, an energy expert at the London-based Center for Global Energy Studies, “to get the Iranians to sit at the table and talk and put in proper monitoring of their nuclear industry. The sanctions aren’t an end in and of themselves.”

Meanwhile, U.S. and European efforts to put a crimp in Iran’s exports appear to be having an effect already.

U.S. restrictions on doing business with Iran’s central bank have been felt in India, the second-largest buyer of Iranian oil. Refiners there are seeking new suppliers after India’s government threatened not to sign a waiver to protect them from U.S. sanctions, according to Lloyd’s List. In addition, Lloyd’s List said, since Iran’s threat to close the Strait of Hormuz, Turkish banks used by Indian refiners to pay for Iranian crude are refusing to transfer those funds.

Japan has also said it would trim its purchases of Iranian oil. Japan imported more than 300,000 barrels a day of oil from Iran in the first 11 months of 2011, according to the International Energy Agency. That provided 10 percent of Japan’s oil imports.

While Iran’s customers are looking for new supplies, Iran is looking for new customers. Oil exports are the country’s main source of income, providing $73 billion of revenue in 2010 and covering half the national budget, according to Energy Department figures.

Lee said Iran was thought to be talking to Venezuelan leader Hugo Chavez about disguising Iran’s oil by mixing it with Venezuela’s. A veteran oil trader in London said Iran could also offer small discounts to tempt independent refiners into buying its crude. He added that Iran could also be looking, as it has in the past, for barter deals such as one in which Cuba might swap sugar for oil.

Iran’s greatest hope for rerouting its exports would be to sell more to its biggest customer, China, which imported about 550,000 barrels a day last year. But a contract dispute has led to a temporary decline in Iranian sales to China. And it isn’t clear how much China wants to rely on one source of oil or how much China can add to its strategic stockpiles.

Some companies will seek waivers to continue to do business with Iran; Japan said it would seek waivers to continue reduced purchases.

Some companies already have waivers. The Italian oil giant ENI has a waiver to continue to receive 10,000 barrels a day of Iranian crude oil as payment for work ENI did on two Iranian fields under old agreements, a company spokesman said. At the current rate, it would take until 2014 for ENI to be fully paid.

Although tensions over Iran may be adding as much as $5 a barrel to the price of oil, according to experts and traders, it is not the only geopolitical factor fueling high petroleum prices.

Nigeria, which produces about 2 million barrels a day, is facing Islamic violence in its north, nationwide protests over the end of fuel subsidies and strikes by major unions. Instability in Libya and Iraq threaten exports there as well.

Moreover, while Saudi Arabia, which produced 10 million barrels a day toward the end of last year, says it can boost output by another couple of million barrels a day to make up for other countries’ lost production, many oil experts fear that the kingdom would be physically unable to do that.

The world’s spare oil production — recently about 4 percent of daily production of 89 million barrels — is important in maintaining stable prices. If sanctions did block Iranian sales, part of that spare capacity would be used.

Deutsche Bank’s Sieminski says he has three “normal” or “standard” worries: “Can the Federal Reserve get the U.S. economy going? Can the Europeans solve their sovereign debt problem? And will China have a soft landing?” He said that, now, “on top of that we have geopolitical concerns mostly related to oil.”

The oil fears are at odds with the others. “With the macroeconomic issues, the worry is that we won’t get enough oil demand. With the geopolitical issues we worry that we won’t have enough oil supply,” he said. As a result, he predicted, “we had a lot of oil price volatility in 2011 and it doesn’t look like 2012 is going to improve much.”