* New deficit estimate is 12.9 pct of GDP

* Weak tax receipts, more government spending blamed

* Republicans, some Democrats already wary of rising debt

(adds background)

By Caren Bohan and Richard Cowan

WASHINGTON, May 11 (Reuters) - The White House on Monday pushed up its forecast for the U.S. budget deficit for this year by $89 billion, reflecting the recession, a raft of new unemployment claims and corporate bailouts.

A fresh estimate of the deficit showed it coming in at $1.84 trillion -- representing a massive 12.9 percent of gross domestic product -- in the current 2009 fiscal year that ends on Sept. 30. A prior White House forecast released in February projected a deficit of $1.75 trillion, or 12.3 percent of GDP.

The report may add to the political challenges facing President Barack Obama as he seeks to push through a new healthcare plan and other big domestic initiatives.

A White House official said the gloomier deficit picture reflected weaker tax receipts as the economy declined and higher costs for social safety-net programs such as unemployment insurance. Spending on the government rescues for the financial and automobile industries was also a factor in the higher deficit, said the official, who spoke to reporters on condition of anonymity.