WASHINGTON - President Obama said Saturday that Republicans in the House were blocking a bill that would prevent a tax increase on the first $250,000 of income earned by all Americans.

The Democratic-controlled Senate has approved the measure, but Obama said House Republicans had "put forward an unbalanced plan that actually lowers rates for the wealthiest Americans." Obama supports a plan to raise taxes on families earning more than $250,000.

In his weekly radio and Internet address, Obama said "the math just doesn't work" in the GOP plan.

Obama's comments marked the fourth time since his reelection that he has used the radio address to push for middle-class tax cuts as part of a plan to avoid the fiscal cliff - and his most sharply partisan tone.

He said his plan to raise taxes on the wealthiest Americans should come as no surprise to Republicans or anyone else.

"After all, this was a central question in the election," he said. "A clear majority of Americans - Democrats, Republicans, and independents - agreed with a balanced approach that asks something from everyone, but a little more from those who can most afford it."

He said his plan was "the only way to put our economy on a sustainable path without asking even more from the middle class." It also is the only plan he is willing to sign, he said.

Obama's comments came as House Speaker John A. Boehner said Friday there had been no progress in negotiations to avoid the fiscal cliff, a combination of automatic tax increases and spending cuts set to take effect in January.

Boehner said the White House had wasted another week and had failed to respond to a GOP offer to raise tax revenue and cut spending. Obama and Boehner spoke privately by phone Wednesday. Boehner described the conversation as pleasant "but just more of the same."

Obama said in his address he was ready to work with Republicans on a plan that spurs economic growth, creates jobs, and reduces the deficit. He said he wanted to find ways to bring down health-care costs without hurting seniors and was willing to make more cuts in programs such as Medicare.

Sen. Marco Rubio of Florida said in the Republican response Saturday that tax increases would not solve the nation's $16 trillion debt. Only economic growth and reform of entitlement programs will help control the debt, Rubio said.