The United States is unprepared for a global decline of conventional oil reserves that could push energy prices sharply higher in the coming decades, the Government Accountability Office said in a report released Thursday.

The GAO’s report to Congress addressed the hotly debated “peak oil” theory, citing a range of forecasts that global oil production might level off or decline anytime between now and 2040.

Although the economic impact would vary depending on when such a peak occurs and how prepared the nation is, the GAO found that the consequences could be dire if oil production declined sharply and viable alternatives were not available. Oil prices would rise sharply, “possibly to unprecedented levels” as nations competed for scarce resources.

“While these consequences would be felt globally, the United States, as the largest consumer of oil and one of the nations most heavily dependent on oil for transportation, may be especially vulnerable among the industrialized nations of the world,” the GAO said.

The report also found that the federal agencies “have no coordinated or well-defined strategy” either to reduce the uncertainty of when such an oil crunch might arrive or to minimize the consequences.

Rep. Roscoe G. Bartlett, R-Md., who co-chairs the Congressional Peak Oil Caucus with Rep. Tom Udall, D-N.M., called the report a “clarion call” for action.

“Only the president can rally the country to take the urgent steps necessary” Bartlett said. “Potential alternatives to oil are extremely limited. Technology won’t save us without time and money to develop and scale them up.”

Some academics and geologists have been suggesting for years that the world is on the brink of a decline in production.

The theory has repeatedly been dismissed, however, by mainstream industry experts who suggest that peak oil theorists have failed to grasp the role that economics and technology will play as conventional reserves decline. Higher prices driven by scarcity of resource will naturally reduce demand, they say, while at the same time making unconventional sources and alternatives more economical.

A November report by Cambridge Energy Research Associates (CERA), an energy consulting firm, suggests that a peak in oil production won’t arrive until at least 2030, and even then the world won’t be hit by a precipitous drop in oil supplies. Rather, production will follow “an undulating plateau” for one or two more decades before starting a gradual decline.

“We hold that above-ground factors will play the major role in dictating the end of the age of oil,” CERA said in its report.

Numerous alternatives to oil are available, and the GAO said the private sector is already responding to higher energy prices by investing in things such as biofuels. But the report said that investment is driven based on price expectations, so the nation cannot guarantee that it will continue unless prices remain high.

Some lawmakers, including Sen. Richard G. Lugar, R-Ind., and Rep. Rick Boucher, D-Va., have proposed creating some kind of price floor for oil to spur further investment in alternative fuels and to ensure that nascent industries don’t collapse if oil prices decline in the future.

The GAO report cited Energy Department figures indicating that alternative technologies such as corn ethanol have displaced only 1 percent of U.S. petroleum consumption to date and are unlikely to make up more than 4 percent of the projected consumption by 2015. With sufficient investments, however, the department estimates that alternative fuels could displace up to 34 percent of the nation’s petroleum consumption by 2030.