The US budget deficit widened over the first 6 months of fiscal 2015 as spending on Social Security & health services increased.  Spending exceeded revenue by $439B from Oct-Mar, compared with a $413B deficit in the same period the prior year, the Treasury Dept reported.  The shortfall in Mar was bigger than been projected.  The deficit is widening even as the economy accelerates.  In the first half of the fiscal year, revenue grew more than 7% to $1.4T, the highest since at least 1998, boosted by higher individual & corp tax receipts.  For Mar, the deficit increased $16B to $52.9B from a year earlier.  Payments to the Treasury from Fannie Mae & Freddie Mac were $15B lower than same month last year, largely because financial institutions made fewer settlement payments to the gov-sponsored enterprises than they did last year, the CBO said last week.  Revenues increased 8.5% in Mar, while spending rose 13.6%.