They raised their 2011 forecast for inflation-adjusted U.S. growth to 2.7% from 1.9%, saying so-called “organic growth” – that not driven by government spending or inventory rebuilding – is taking off.

Wednesday’s change puts Goldman’s GDP forecast above the Wall Street consensus for the first time in five years, Goldman economist Jan Hatzius said.

He said in a conference call with investors and the media that the firm is seeing evidence that private sector deleveraging — the process in which households and businesses pay down debt rather than spend on goods and services — is starting to slow, giving support to what has been anemic U.S. demand.

“This is a pretty important shift,” Hatzius said. “This is why are we turning more upbeat on U.S. growth after being downbeat for the past five years.”

Hatzius said recent months have shown a marked increase in organic growth, in a reversal of the initial stages of the economic rebound in 2009. He said that the vast majority of the 5% year-over-year expansion in inflation-adjusted economic output seen at this time last year was attributable to fiscal stimulus and inventory effects.

But with fiscal spending now slowing to a trickle and rebuilt inventories now exerting a drag on growth, organic growth is taking root, Hatzius said.

He said organic growth is now on track to rise at a 5% annualized rate, compared with something on the order of half that including the fiscal and inventory effects.

Goldman also halved its view of the size of the Fed’s quantitative easing program, in which the central bank buys bonds to support weak U.S. demand. Goldman has been saying it expects $2 trillion worth of asset purchases, but Hatzius said Wednesday the firm has now slashed that target to $1 trillion as U.S. numbers firm up.