Federal Reserve officials, who are expected to raise interest rates next month, are already sketching out positions for a post-liftoff debate that may blur the lines between inflation “hawks” and “doves” and make the Fed’s policy less predictable. Fed officials’ private and public comments show that the debate now centers on whether the U.S. economy is returning to its old robust self, or whether tepid growth and resulting weak inflation and slow wage increases have become the new norm after the deep recession of 2007-2009.