ARLINGTON, Virginia (Reuters) - The White House will respond to "any serious offer" from congressional Republicans to prevent the U.S. "fiscal cliff" and "theoretically" could negotiate how much tax rates must rise for top earners, Vice President Joe Biden said on Friday.

Biden, who was meeting with people at a diner who described how an increase in middle-class tax rates would affect them, laid out two criteria for a deal to avoid looming spending cuts and across-the-board tax hikes: an increase in tax rates for the wealthiest Americans and an end to political gamesmanship over raising the debt ceiling.

"The president's ready to respond to any serious offer put on the table," Biden told reporters when asked to respond to Republican Speaker of the House of Representatives John Boehner's comment that President Barack Obama was pushing the country toward the fiscal cliff.

"That is not the president's position," Biden said. "We have laid out where we are. There has been in a sense a referendum" on the need for higher tax rates for the wealthiest Americans and for an end to stalemates over the debt ceiling, he said.

The White House wants tax rates for the top 2 percent of U.S. earners to go up as part of a fiscal cliff deal. Obama has said Republican leaders must accept that reality in order to reach an agreement, but Biden indicated some flexibility on how high tax rates for the wealthy would have to rise.

"The top brackets have to go up," he said. "Theoretically, we can negotiate how far up, but we think it should go - the top rate should go to 39.6 percent."

He said the administration was ready to negotiate reform to entitlement programs and look at more spending cuts, but believed that revenue in a final package had to be in the range of $1.7 trillion over 10 years.

Biden pressed the administration's case that Congress should agree now to extend tax cuts for middle-class Americans and separate that from the debate over rates for the wealthiest.

"It would take 15 minutes from the time the decision was made by the speaker of the House to pass and make permanent the middle-class tax cut, the president would probably have me sprint up to the Hill to bring the bill down for him to sign," he said.

"It is not complicated, and it doesn't even require our Republican friends to say, 'we agree that we should raise taxes on the top 2 percent.'"

He forecast that if both sides "act like adults" and can compromise, economic growth will strengthen. The U.S. economy, which added 146,000 jobs in November, had turned a corner and was moving in the right direction, Biden said.

(Additional reporting by Mark Felsenthal; Editing by Eric Beech)