Hersh, the veteran investigative reporter who uncovered the My Lai massacre in Vietnam more than 40 years ago, wrote in the latest issue of The New Yorker magazine that President George W. Bush was running a secret $400 million project to topple the Islamic Republic in Iran. He also claimed that U.S. Special Operations Forces based in southern Iraq had been carrying out secret commando raids into neighboring Iraq since 2007 with Bush's official approval.

The White House refused to issue any comment on the article, and so did the CIA. But Ryan Crocker, the U.S. ambassador to Baghdad, while not denying Hersh's claim of the $400 million secret program, focused on shooing down the claim that U.S. forces had been operating within the territory of the Islamic Republic.

"I can tell you flatly that U.S. forces are not operating across the Iraqi border into Iran, in the south or anywhere else," Crocker told CNN in an interview. "U.S. forces are not operating across the Iran-Iraq border, no."

Also on CNN, Hersh countered by saying that while he believed Crocker could be telling the truth, it was routine in such situations for U.S. envoys not to be informed when such operations were being undertaken to maintain security and deniability.

"Sometimes it's better not to have the ambassador know," Hersh said. He claimed that U.S. forces based in Afghanistan where they are fighting the resurgent Islamist Taliban had also carried out incursions into Iran.

According to Hersh's New Yorker article, his claims will not spark any angry investigation by the Democrat-controlled 110th Congress because Democratic leaders on Capitol Hill were informed of the operations in advance and approved them.

If Hersh's report is confirmed, it could increase tensions between the United States and Iran and the dangers of an outbreak of hostilities between them: Fears that the U.S. Air Force or the Israelis will launch a pre-emptive air attack on Iran's nuclear facilities before President Bush leaves office in January 2009 are regarded as one of the most powerful forces propelling global oil prices and domestic U.S. gasoline prices to record levels. The global oil price hit a new high of more than $142 a barrel last week.

Hersh's article was also significant because it claimed that senior U.S. Army generals had opposed the policy of seeking to destabilize Iran.

The U.S. Army and Marine Corps currently have around 160,000 troops operating mostly in central Iraq, where they have enjoyed considerable success in the past year and a half in suppressing extreme Islamist guerrillas operating in the center of the country. However, the land supply lines for the U.S. ground forces in Iraq go through the south of the country, where 60 percent of Iraq's Shiite majority lives. A full-scale war between the United States and Iran runs the risk of inciting the Shiite militias that control southern Iraq to try and cut off those roads for U.S. Army supply columns.

The three most recently retired four-star heads of U.S. Central Command, which directs military operations in the Iraq theater, have all publicly opposed any pre-emptive air attack on Iranian nuclear facilities. They are Adm. William "Fox" Fallon, Gen. John Abizaid and Gen. Anthony Zinni.

Most Middle East experts are highly skeptical that Iranians would support exiled dissident groups and leaders that the Bush administration has been favoring. They note that similarly unrealistic hopes surrounded the Iraqi National Congress of Ahmed Chalabi. Senior Bush policymakers were convinced before the 2003 invasion to topple Iraqi dictator Saddam Hussein that millions of Iraqis would flock to Chalabi's support. They didn't.