WASHINGTON — President Barack Obama said Friday Congress has a “unique opportunity to do something big” and stabilize the economy by cutting deficits even as it raises the national debt limit to avert an unprecedented U. S. default.

Saying he was ready to make tough decisions and challenging Republicans to do the same, Pres. Obama attempted to turn the Republicans’ opposition to any tax increases back against them, warning that failure to raise the debt ceiling would mean “effectively a tax increase for everybody.”

Administration officials and private economists say that if the U. S. fails to raise its borrowing limit by Aug. 2 and begins to stop paying its bills as a result, the fragile U. S. economy could be cast into a crisis that would reverberate around the globe.

The United States hit its current $14.3 trillion debt ceiling in May and has been juggling its books since then. Republicans, who control the House of Representatives, say they won’t raise the debt limit unless Democrats agree to major spending cuts to reduce the spiraling U. S. deficit.