"Our job is to actually help the Iraqis generate the forces and the support necessary for operations in Mosul and we'll be ready for that in October," Dunford told a small group of reporters traveling with him.
"The noose is gradually tightening around Mosul," he added.
The city, Iraq's second-largest, is ISIS' last significant stronghold in the country. It and Syria's Raqqa -- the group's self-declared capital -- are the major targets left for the US-led coalition to take back from its control.
Dunford's statement is the clearest sign from a senior US military official that the military battle for Mosul could soon begin once the Iraqis make the political decision to proceed. It also means the battle for Mosul may be raging during the US presidential election, with US forces facing dangers on the battlefield. Those troops might also be called upon to help begin providing humanitarian aid.
Dunford, along with Defense Secretary Ash Carter, is scheduled to testify before the Senate Armed Services Committee Thursday. Both are expected to face stiff questioning from Republicans on the panel about the Obama administration's strategy to fight ISIS.
CNN has learned the Pentagon is now considering setting up new remote bases well outside Mosul as hubs from which US forces can operate.
Those types of bases, given their locations, are likely to be less secure than the large bases the US has generally been using. They could be used by US military advisers who are expected to work with the Iraqis in the field.
Because of the remote locations, security may be difficult. US forces may move "in and out" of the bases rather than locate there consistently, one official said. These bases are in addition to the large Iraqi base south of Mosul at Qayyarah, where hundreds of US troops are already located to assist with supplies, logistics and support for the Iraqi forces.
A key decision to be made is whether additional US conventional and special operations forces will be needed for ensuring the Iraqis succeed, several US defense official told CNN. The US forces will not be on the front lines but will be out in the field with Iraqi units, officials said.
Some forces already in Iraq could be reassigned to northern Iraq, or additional forces could be sent.
President Barack Obama and Iraqi Prime Minister Haider al-Abadi's meeting in New York Monday also signaled the Mosul operation may soon unfold.
"We feel confident that we will be in a position to move forward fairly rapidly," Obama said. Calling Mosul a "challenging battle," Obama also noted that the US will be "prepared to help provide rapid humanitarian assistance" to displaced Iraqis.
Abadi underscored the urgency.
"We hope within the next few months we're going to kick Daesh out of Mosul and we'll deliver a huge blow to what Daesh believes in," said Abadi, using another name for the terrorist group.