Donald Rumsfeld, the US defence secretary, recently asked Abizaid to stay for a year beyond this summer, when he will have completed the normal three-year stint as commander, and he agreed.

Bryan Whitman, a Pentagon spokesman, said: "General Abizaid is doing important work and has indicated that he wants to continue doing it. Secretary Rumsfeld appreciates that General Abizaid wants to continue, and there are no plans to replace him."

Abizaid has won praise for his work, even as Rumsfeld and George Bush, the US president, have come under fire from congressional Democrats and other critics for the war.

He travels frequently to Pakistan, Saudi Arabia and other countries in the region that the Bush administration considers to be important allies in the war on terror.

A central feature of Abizaid's approach in Iraq has been forcing the Iraqis to take more responsibility for their security, arguing that the longer US troops carry the heavier load, the more dependent the Iraqis will become.

Rumsfeld often makes the same argument, saying US troops must put more Iraqis in the lead of the fight against the insurgents even at the risk of seeing them falter or fail.

Asked in an interview last week whether he had foreseen the protracted nature of the insurgency there, Abizaid said, "People who think that ... institutions of a country like Iraq that was run by Saddam Hussein for 30 years were going to be fixed quickly or easily just were never correct, and it's clear that it takes a lot of time."

Long war

Abizaid is generally credited with coining the phrase "Long War" to describe a global struggle against Islamic extremism - a fight he says includes not only prevailing in Iraq and Afghanistan but also countering ideological support for terrorism globally.

Most of Abizaid's predecessors served three-year tours, but there is no set tenure.

Abizaid took the job in July 2003, replacing Army General Tommy Franks, who drew up and executed the Afghanistan and Iraq invasion plans. Around the time Franks left, the Iraqi insurgency began to take hold, marking an unexpected turning point in a conflict that the Bush administration had expected to last months, not years.

In January 2003, two months before the invasion, Rumsfeld plucked Abizaid from his post as director of the Joint Staff in the Pentagon to make him a deputy commander of Central Command, under Franks.

The extension of Abizaid's tenure through summer 2007 would make him the longest-serving commander in the 23-year history of US Central Command.