WASHINGTON (Reuters) - Deficit-reduction legislation offered by Senate Democrats, which also increases U.S. borrowing authority, would cut $2.2 trillion from deficits, about $500 billion less than Democrats claimed, the Congressional Budget Office said on Wednesday.

The non-partisan budget analyst for Congress also confirmed that about half of the Democrats' proposed savings would come from reduced costs as the United States withdraws from the wars in Iraq and Afghanistan.

On Tuesday, the CBO said the Republican plan proposed by House Speaker John Boehner would cut spending by $850 billion over 10 years, rather than the $1.2 trillion as the bill promised.

(Reporting by Richard Cowan and Deborah Charles)