"We're in a position where a vast majority of the work has been done," Earnest said in response to a question from TIME's Zeke Miller. "The bulk of the work has been done."
"That [remaining] work will be done in sufficient time for the President to make an announcement before the end of the year," he added. "There are still some additional decisions that need to made."
Earnest also said President Obama has been working with Attorney General Eric Holder at the Justice Department and Homeland Security Secretary Jeh Johnson "for months" to form decisions about what action to take on the issue. He has also been taking suggestions from outside groups.
Last week the White House announced President Obama will delay executive action on illegal immigration until after the 2014 midterm elections in an effort to save vulnerable Democrats from voters. Obama had originally promised to use executive action on the issue by the end of the summer.
This post has been updated.