As he barnstorms across the country campaigning for Republican candidates in Tuesday's elections, Bush has been citing oil as a reason to stay in Iraq. If the United States pulled its troops out prematurely and surrendered the country to insurgents, he warns audiences, it would effectively hand over Iraq's considerable petroleum reserves to terrorists who would use it as a weapon against other countries.

"You can imagine a world in which these extremists and radicals got control of energy resources," he said at a rally here Saturday for Rep. Marilyn Musgrave (R-Colo.). "And then you can imagine them saying, 'We're going to pull a bunch of oil off the market to run your price of oil up unless you do the following. And the following would be along the lines of, well, 'Retreat and let us continue to expand our dark vision.' "

Bush said extremists controlling Iraq "would use energy as economic blackmail" and try to pressure the United States to abandon its alliance with Israel. At a stop in Missouri on Friday, he suggested that such radicals would be "able to pull millions of barrels of oil off the market, driving the price up to $300 or $400 a barrel."

Oil is not the only reason Bush offers for staying in Iraq, but his comments on the stump represent another striking evolution of his argument on behalf of the war. The slogan of "no blood for oil" became a rallying cry for antiwar activists prior to the March 2003 invasion and angered administration officials. "There are certain things like that, myths, that are floating around," Rumsfeld told Steve Kroft of CBS Radio in November 2002. "It has nothing to do with oil, literally nothing to do with oil."

White House spokesman Tony Fratto said Saturday that Bush's latest argument does not reflect a real shift. "We're still not saying we went into Iraq for oil. That's not true," he said. "But there is the realistic strategic concern that if a country with such enormous oil reserves and the corresponding revenues you can derive from that is controlled by essentially a terrorist organization, it could be destabilizing for the region."

Some analysts, however, said that Bush is exaggerating the impact of Iraq's oil production on world markets. Iraq has more than 112 billion barrels of oil, the second-largest proven reserves in the world. But it currently pumps just 2.3 million barrels per day and exports 1.6 million of that, according to the State Department's tracking report on the country, still short of what it produced before the invasion.

That represents a fraction of the 85 million barrels produced around the world each day and less than the surplus capacity of Saudi Arabia and other Organization of Petroleum Exporting Countries, meaning in a crisis they could ramp up their wells to make up for the shortfall, analysts said. The United States also has 688 million barrels of oil in the Strategic Petroleum Reserve, enough to counter a disruption of Iraqi oil for 14 months.

Even if Iraq did not sell oil to the United States, it would not matter as long as it sold it to someone because the international market is fungible and what counts is the overall supply and overall demand, according to analysts. If Iraq cut off exports altogether, it still would not have the dire effect on the world market that Bush predicts, they said. The price of oil began rising dramatically in 2002 as the confrontation with Iraq loomed, but many factors contributed, including increasing demand by China and problems in Nigeria, Venezuela and elsewhere.

The world, in fact, has already seen what would happen if Iraqi oil were cut off entirely, as Bush suggests radicals might do. Iraq effectively stopped pumping oil altogether in the months immediately after the invasion. And yet the price of oil has never topped $80, much less come anywhere near the $300 or $400 a barrel Bush cited as a possible consequence of a radical Iraqi regime withholding the country's oil.

"They're a minor exporter," said Edward Morse, managing director and chief energy economist at Lehman Brothers. "They have potential to be a greater exporter. But it's ludicrous to suggest someone could hold the world hostage by withholding oil from the market, especially a regime that needs money."

Disruptions of oil supplies certainly affect the markets, but not as drastically as Bush suggested, Morse said. He noted that Venezuela's capacity has fallen by 1 million barrels a day since President Hugo Chavez came to power there and yet it has not given him any geopolitical leverage over the United States even though he is an avowed Bush foe. But Morse agreed that Iran, for example, could "play mischief" because it already effectively controls much of Iraqi oil in the southern part of the country.

Fratto, the White House spokesman, argued that even if radicals could not move the markets dramatically with Iraqi oil, they would use the country as a base to topple other governments in the Middle East such as Kuwait and Saudi Arabia, which would give them "a lot more oil to blackmail with."