Secretary of State Rex Tillerson said Tuesday that his plan to reduce the size of the State Department staff will come at the expense of civil servants more than overseas diplomats and staff.

"It's being managed in a very deliberate way, but being mindful of not diminishing the strength of our foreign service officers," Tillerson told the Senate Foreign Relations Committee.

Tillerson said he expects an eight percent cut in State Department employees — about 2,300 jobs, according to other reports — by the fall of 2018. But that won't be divided evenly between the foreign service officers and civil servants.

"Foreign service is only going to be down about four percent," Tillerson said. "Civil servants are going to be down about 12."

The workforce reduction will be part of an overall reorganization of the State Department, involving the streamlining of some bureaus or agencies and potentially the elimination of others. Tillerson told lawmakers that the plan would be fleshed out through the summer and fall, making it difficult to describe in detail at today's budget hearing. But he emphasized that the staff cuts would be phased in gradually.

"What we're doing is just allowing normal attrition to bring the numbers down," Tillerson said. "As we look ahead we'll probably be looking at a one-for-three kind of replacement [rate]."