Clearly the answer lays in two parts, increasing revenue and decreasing spending.
Without defaulting on the debt, there are two areas of spending, discretionary with is about 40% of the budget and the ever increasing entitlements that are 60%. And defaulting on the debt payments would make little practical difference with the budget in the shape it is in.
Now, if we kept entitlements the same as they are now - froze them - we would have $150 billion to parcel out for defense and all domestic and international policies, plans and spending. That is foreign aid, disaster relief at home and abroad, jobs programs, payments ot local governments, science, global warming, roads, education, alternate energy, NASA, farm aid programs, WIC, some unemployment plans and all of defense. Also FBI, National Security, Air Traffic Control, Customs, immigration, Justice Dept, Prisons, CIA, counter-terrorism, EPA, BATF, and all the rest. SEC, Secret Service, Treasury Dept, Army Corps of Engineers, White House operations and everything.
To make the budget balance out of "discretionary spending" we would have to slash every program on average about 85%.
On the entitlement side, we have about 60% of the total government spending. And even so, the current program is not spending as much as it is SUPPOSED to. (Medicaid/medicare not reimbursing like it is supposed by law). And this side of governement spending has been growing faster than the rest put together (even including the "stimullus" package) over time.
If one were to take the hard core conservative approach or the libertarian appraoch and cut $100 billion out of the $670 billion in discretionary spending, that would still be a drop in the bucket.