WASHINGTON — Al Qaeda’s organization in Iraq may suffer a credibility crisis now that American officials have learned that the head of Al Qaeda’s shadow state in Iraq is a fiction.

Yesterday, Brigadier General Kevin Bergner said a captured senior leader of the group — Fatah Da’ud Mahmud al-Mashadani — has confessed that for more than a year, the Islamic State of Iraq, Al Qaeda’s governance wing, has put forward an imaginary Iraqi named Umar al-Baghdadi as the group’s political leader. The terror organization’s deputy leader, Ayman al-Zawahri, even addressed the nonexistent Mr. Baghdadi in speeches.

But it was all a ruse, General Bergner said at a press conference yesterday for the Arabic and American press, and the voice of Mr. Baghdadi was actually that of an Iraqi radio actor named Abu Abdullah al-Naima. Mr. Naima pretended to be Mr. Baghdadi and reported to the Egyptian chief of Al Qaeda in Iraq, Abu-Ayub al-Masri, the American general said, citing information gleaned during the interrogation of Mr. Mashadani, a man described as the most senior Iraqi terrorist in Al Qaeda’s Iraq branch.

The emergence of Umar al-Baghdadi was intended to make it appear that Al Qaeda in Iraq was now being headed by an Iraqi — a strategic shift for the group founded by the late Abu Musab al-Zarqawi, who hailed from Jordan. In an October 2005 letter, Mr. Zawahri urged Zarqawi him to include more Iraqis so as not to alienate the population.

“We don’t want to repeat the mistake of the Taliban, who restricted participation in governance to the students and the people of Kandahar alone. They did not have any representation for the Afghan people in their ruling regime, so the result was that the Afghan people disengaged themselves from them,” he wrote.

General Bergner added: “Mashadani confirms that al-Masri and the foreign leaders with whom he surrounds himself, not Iraqis, make the operational decisions for AQI. To be clear, Al Qaeda-Iraq is run by foreigners, not Iraqis.”

He also said yesterday that Mr. Mashadani had disclosed that many of the operational decisions of Al Qaeda in Iraq were made by the group’s senior leadership.

In the psychological war with Al Qaeda, the news could be a death knell for the organization’s aspirations to establish a branch of the Islamic Caliphate in Iraq. And an Iraqi government official said many Iraqis were still digesting the news.

“The tide is turning on Al Qaeda and has been for some time. But if this story turns out, it could be a final blow,” the official said, speaking on condition of anonymity.

The news from the capture could also help bolster Republicans in Washington who yesterday fended off the latest efforts from Senate Democrats to force a vote on withdrawal from Iraq.

After debating defense authorization legislation through Tuesday evening, the majority leader, Senator Reid, a Democrat of Nevada, withdrew the bill after he could only muster 52 votes to end the debate — eight short of the 60 votes needed.

Mr. Reid said he might bring up the defense authorization bill at another point in the Senate legislative calendar, but it is likely that the debate over withdrawal amendments will not resume until September when the White House is expected to ask for additional funds for the wars in Afghanistan and Iraq.