WASHINGTON — President Barack Obama is prepared to veto legislation to block year-end tax hikes and spending cuts, collectively known as the “fiscal cliff,” unless Republicans bow to his demand to raise tax rates for the wealthy, administration officials said.

Freed from the political and economic constraints that have tied his hands in the past, Obama is ready to play hardball with Republicans, who have so far successfully resisted a deal to tame the debt that includes higher taxes, Obama’s allies say.

In the days after the November election, the tables will be turned: Taxes are scheduled to rise dramatically in January for people at all income levels. If he wins reelection, Obama may finally be able to dictate the terms of a bipartisan debt-reduction deal. And if he loses to Republican Mitt Romney, Obama could make sure that tax rates rise before he hands over the keys to the White House on Inauguration Day in late January.