By ANDREW TAYLORWASHINGTON (AP) â¿¿ House Speaker John Boehner said Wednesday that "serious differences" remain between him and President Barack Obama in negotiations on averting automatic spending cuts and tax increases that economists say could send the U.S. economy over a "fiscal cliff." Boehner's comments came as top Democrats pushed back on GOP demands for tough steps such as raising the Medicare eligibility age and curbing the cost-of-living adjustment for Social Security. Boehner and Obama spoke on the phone Tuesday, a day after the president offered to reduce his initial demand for $1.6 trillion in higher tax revenue over a decade to $1.4 trillion. But Obama continues to insist that much of the revenue come from raising top tax rates on the wealthy. Boehner countered later Tuesday with another offer that GOP aides said stuck close to a document delivered to the White House a week ago. A top White House aide, Rob Nabors, came to the Capitol to respond. A Democratic official said Boehner's counter-offer included permanent extension of Bush-era tax rates for all taxpayers including the top 2 percent of earners, the same as his earlier proposal. Boehner offers $800 billion in new revenues through a tax reform measure next year. The officials spoke only on condition of anonymity because they were not authorized to describe the private talks. Boehner on Wednesday offered a sour assessment less than three weeks before the cliff deadline. The changes would strike the economy with $500 billion worth of spending cuts and higher tax rates if left in place through September. "There were some offers that were exchanged back and forth yesterday and the president and I had pretty frank conversations about just how far apart we are," the Ohio Republican said after a closed-door meeting with fellow GOP lawmakers in which he advised them not to make plans for the week after Christmas.