The Federal Reserve Board has expanded its $600 billion Main Street Lending Program to serve much smaller businesses. The program — first announced as part of the Fed’s larger $2.3 trillion package of loan and bond initiatives — now has lower loan limits, with a minimum size of $250,000. That’s down from a $500,000 limit announced in May, also lowered at that time. The loan terms have also been lengthened from four years to five years, according to an announcement Monday by the Federal Reserve.