WASHINGTON - President Barack Obama will challenge government agencies to cut $100 million in spending when he holds his first Cabinet meeting on Monday, an administration official said.

Agencies will be required to report back with their savings at the end of 90 days, the official said.

Republicans have accused the president and the Democratic-controlled Congress of wasteful spending, saying Obama's $3.5 trillion 2010 budget plan carries too much deficit spending and too few tax cuts.

The United States posted a record $956.8 billion budget deficit for the first half of fiscal 2009, more than three times the shortfall of a year ago, the Treasury Department reported earlier this month.

Much of the deficit was caused by spending on financial and economic rescue programs aimed at propping up companies whose collapse could worsen the global recession.

Without significant change to steer away from ever-expanding deficits and debt, we are on an unsustainable course, Obama said in his weekly radio address on Saturday.

The administration official said that in asking his Cabinet to find the $100 million in spending cuts, he would point to examples of savings that government agencies had already begun to implement.

The Department of Homeland Security estimated that it could save up to $52 million over five years by buying office supplies in bulk, the official said.

Obama has vowed to halve the United States' deficit, to $533 billion, by 2013.