WASHINGTON — In a major shift of focus in the battle against the Islamic State, the Obama administration is planning to establish a new military base in Anbar Province and send 400 American military trainers to help Iraqi forces retake the city of Ramadi.

Although a final decision by the White House has yet to be announced, the plan follows months of behind-the-scenes debate about how prominently plans to retake another Iraqi city, Mosul, which fell to the Islamic State last year, should figure in the early phase of the military campaign against the group.

The fall of Ramadi last month effectively settled the administration debate, at least for the time being. American officials said Ramadi is now expected to become the focus of a lengthy campaign to regain Mosul at a later stage, possibly not until 2016.

The United States Central Command’s emphasis on retaking Mosul depended critically on efforts to retrain the Iraqi Army, which appear to have gotten off to a slow start. Some Iraqi officials also thought the schedule for taking Mosul was unrealistic, and some bridled when an official from the Central Command told reporters in February that an assault to capture the city was planned for this spring.