Oct 5 (Reuters) - U.S. Treasury Secretary Janet Yellen on Tuesday said it was “utterly essential” for Congress to lift the federal debt limit ahead of an October 18 deadline afterwhich failure to do so would trigger a first-ever U.S. default. Asked during an interview on CNBC if she would back a process called “reconciliation” for getting the limit increased without any Republican support, Yellen said: “I support getting it done.” (Reporting By Dan Burns and David Lawder)