"There is no decision to pull out early, indeed quite the contrary," Donald Rumsfeld told American troops he was visiting in the Pacific island of Guam on Friday.
"We will stay there as long as necessary to see that country is put on a path to democracy," the defence secretary stressed.
Rumsfeld's remarks come amid escalating resistance attacks on US-led occupation troops in Iraq, forcing a major policy-rethink in Washington.
Rumsfeld acknowledged the initial US-plan had been for a transfer of sovereignty after a new Iraqi constitution had been ratified and elections held.
But the process would have taken about two years and Rumsfeld said the US would now try to find a way of transferring some responsibility before that.
"It does not mean that we would physically leave the country any sooner," Rumsfeld explained.
"What it means is that the Iraqis would begin to take on a greater portion of responsibility for governing themselves sooner than the original thought was with respect to first a constitution, then national elections because of the time involved," he said.
The Defence Secretary was in Guam on his way to a week-long tour of South Korea and Japan.
He was to hold talks with Japanese Prime Minister Junichiro Koizumi later during the day against a backdrop of growing Japanese reluctance to contribute troops to Iraq.
A day after a bomb attack killed 18 Italian policemen in southern Iraq on Wednesday, Japan postponed its troop deployment plan in view of the deteriorating security situation.