A Reuters poll taken Wednesday after the Fed's latest two-day policy meeting showed primary dealers, the banks authorized to trade directly with the Fed, were uniform in the view that policy makers would forego an interest rate hike at their next meeting, on Sept. 19-20.

But all 17 of the 23 dealers answering the survey said policy makers will unveil the start date and other remaining particulars needed to begin winding down the Fed's holdings of more than $4.2 trillion of Treasuries and mortgage-backed securities. The results were broadly in line with a poll taken last month.

The Fed, as expected, left interest rates unchanged on Wednesday and signaled that the balance sheet reduction process would begin "relatively soon." Policy makers last raised rates at their June meeting, lifting rates by a quarter percentage point to a range of 1.00 percent to 1.25 percent.

The June increase was the fourth by the Fed since it started the process of normalizing its monetary policy in December 2015. To that point, it had held its benchmark overnight lending rate in a range of zero percent to 0.25 percent for seven years as the US economy struggled through and slowly emerged from the Great Recession.

Fifteen of the 17 primary dealers in the survey anticipate the Fed's next rate rise will occur at its December meeting, when they expect another quarter point increase, to a range of 1.25 percent to 1.50 percent. Two dealers see the Fed standing pat then, and financial futures markets assign less than a 50 percent probability of the Fed getting in another rate hike this year as it faces headwinds from stubbornly low inflation.

The primary dealers were more divided in their opinion of how high rates will be by the end of 2018, with views spanning from as low as a range of 1.50 percent to 1.75 percent, to a range as high as 2.25 percent to 2.50 percent. The median view of the group is that rates will end 2018 in a range of 2.00 percent to 2.25 percent.

The US central bank built its massive bond holdings through three rounds of so-called quantitative easing that kicked off during the financial crisis. In all, it acquired roughly $3.75 trillion of Treasuries and mortgage-backed securities in a bid to support an economic recovery by keeping long-term interest rates low.

The bank plans to slowly unwind a sizeable but still-undetermined portion of that portfolio by ending its practice of reinvesting the proceeds it receives from interest payments and the principal from maturing securities.

Initially, under plans previously announced, the Fed will slow those reinvestments at a pace of $6 billion less of Treasuries purchased each month and $4 billion less of MBS. That pace will grow in quarterly increments until it reaches a so-called terminal rate of $30 billion less a month for Treasuries and $20 billion less a month for MBS.