* Obama says spending cuts "send a signal"
* Republicans mock move as publicity stunt
* Obama's Cabinet now almost complete (Updates with Obama speaking, Republican reaction)
By Ross Colvin
WASHINGTON, April 20 (Reuters) - President Barack Obama challenged U.S. government departments on Monday to find $100 million in savings, but the move was mocked by critics who said the government spent that amount in just 13 minutes.
Obama, who has vowed to cut the country's ballooning deficit in half by 2013, told his Cabinet at their first meeting to identify the spending cuts and report back in three months.
Asked by a reporter after the meeting if the $100 million was not just a drop in the bucket, Obama acknowledged it was, saying: "$100 million there, $100 million here. Pretty soon, even in Washington, it's going to add up to real money."
He said his government had launched a number of initiatives to cut spending, which has exploded as his administration grapples with the worst economic crisis in decades.
"None of these savings by themselves are going to solve our long-term fiscal problems, but taken together they can make a difference, and they send a signal that we are serious about changing how government operates," Obama said.
But opposition Republicans derided the publicity given by Obama's Democrat administration to the $100 million savings drive, saying the government was projected to spend $4 trillion this fiscal year alone.
"That works out to $7.6 million in spending per minute. It will take about 13 minutes for the federal government to spend $100 million," Congressional Republicans said in a statement.
DEFICIT SPENDING
Republicans have accused Obama and Democrats in Congress of wasteful spending, saying the $3.6 trillion 2010 budget plan carries too much deficit spending. The United States posted a record $956.8 billion budget deficit for the first half of fiscal 2009 that began last Oct. 1, the Treasury Department has said.
"I appreciate the efforts to save millions by identifying unnecessary or duplicative government spending. But let's not forget that at the same time they're looking for millions in savings, the president's budget calls for adding trillions to the debt," Senate Minority Leader Mitch McConnell said.
The Obama administration has repeatedly stressed that it inherited a $1.3 trillion deficit from the Bush administration and that much of the current spending has been to fund financial and economic rescue programs.
White House spokesman Robert Gibbs, however, found himself on the defensive over the $100 million plan at his daily news briefing when he faced questions over whether the normally media-savvy administration had stumbled in highlighting the effort to cut what amounts to a tiny fraction of the deficit.
"Only in Washington D.C. is 100 million not a lot of money ... It is for hundreds of millions of people," Gibbs said.
Obama's first Cabinet meeting on Monday had one person missing -- Kansas Governor Kathleen Sebelius, his nominee for health secretary. The Senate Finance Committee is expected to vote on her nomination on Tuesday. The Senate is expected to act on the nomination quickly.
(Additional reporting by Matt Spetalnick, Richard Cowan, Thomas Ferraro and Donna Smith, editing by Philip Barbara)