The Treasury Department is the federal government’s main paymaster. In fiscal 2010, it made almost 1.1 billion payments. That's about 88 million a month, with about 80 percent being direct electronic deposits into banks and the rest paper checks. The largest share (69.6 million a month in 2010) covers federal benefits, including Social Security (54.2 million), veterans’ benefits (4.1 million) and civil service retirement (2.6 million). Other big classes of payments include government vendors — from cafeteria services to car companies — that receive 1.4 million checks a month and a “miscellaneous” category of 2.5 million payments that finance Medicare and Medicaid payments, grants to state and local governments and payments to investors in Treasury securities. The final large category of payments is tax refunds. In 2010, they totaled about 10 million a month, though in practice they’re bunched around the April 15 tax filing date.

The Defense Department and the Postal Service pay most of their own bills, though they draw their funds from the same Treasury accounts at the Federal Reserve, which acts as the government’s transfer agent.
     Second: Who would — and wouldn’t — get paid if the debt ceiling wasn’t raised and the government couldn’t borrow? Good question. The Treasury hasn’t said what, if any, contingency plan it has devised, and has consistently argued that any attempt to “prioritize” payments is unworkable and could not avoid a government default. One way or another, it would be a mess.