Paul Ryan won't back down

Rep. Paul Ryan with a copy of his budget plan.

NEW YORK (CNNMoney) -- Republican budget guru Paul Ryan is not backing down.

The House Budget Committee chairman mounted a defense of his controversial plan for federal spending in a speech to the Economic Club of Chicago on Monday.

Ryan's plan would cut spending by $6 trillion over the next decade, lower the highest tax rate to 25% and overhaul Medicare and Medicaid. His budget, which has already been approved by the House, would turn Medicare into a voucher program for Americans under 55, or what Ryan calls a "premium-support model."

Democrats don't like much about the overall plan and have started using the changes to Medicare as a political battering ram against Republicans.

On Monday, Ryan answered his critics.

"Our plan is to give seniors the power to deny business to inefficient providers," he said. "Their plan is to give government the power to deny care to seniors."

And to charges that his plan would scale back the social safety net, Ryan said those programs are threatened by rising debt.

"Mounting debt also threatens our poorest and most vulnerable citizens, because those who depend most on government would be hit hardest by a fiscal crisis," he said. "We have to repair our safety net programs so that they are there for those who need them most."

And Ryan employed a political buzzword -- class warfare -- to describe the way President Obama talks about his own debt plan, one that would hike taxes on the nation's top earners.

"Class warfare may be clever politics, but it is terrible economics. Redistributing wealth never creates more of it ... Sowing social unrest and class envy makes America weaker, not stronger," he said.

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Ryan also tackled the debt ceiling. He backed House Speaker John Boehner's calls for spending cuts that exceed the size of the debt ceiling increase.

"For every dollar the president wants to raise the debt ceiling, we can show him plenty of ways to cut far more than a dollar of spending," Ryan said. "Given the magnitude of our debt burden, the size of the spending cuts should exceed the size of the President's debt limit increase."

Earlier on Monday, Treasury Secretary Tim Geithner told Congress that the U.S. government hit the debt ceiling. Geithner told Congress that he estimates he has enough legal hoop-jumping tricks to cover them for another 11 weeks or so.