WASHINGTON — The Federal Reserve announced an unconventional plan on Wednesday to reduce borrowing costs for businesses and consumers, trying once more to spur economic growth despite urgings from Republicans that it refrain from any expansion of its stimulus program.

The Fed said that it would invest $400 billion in long-term Treasury securities over the next nine months, using money raised by selling its holdings of short-term federal debt, in an attempt to drive down interest rates on mortgage loans, corporate bonds and other forms of credit.  Read more