WASHINGTON, May 29 (Reuters) - The top ten U.S. tax deductions, credits and exclusions will keep $12 trillion out of federal government coffers over the next decade, and several of them mainly benefit the wealthiest Americans, a new study from the Congressional Budget Office shows.

The top 20 percent of income earners will reap more than half of the $900 billion in benefits from these tax breaks that will accrue in 2013, the non-partisan CBO said on Wednesday.

Further, 17 percent of the total benefits would go to the top 1 percent of income earners -- families earning roughly $450,000 or more. The same group that was hit with a tax rate hike in January.

The benefits of preferential tax rates on capital gains and dividends, a break worth $161 billion this year, go almost entirely to the wealthy, including 68 percent to the top one percent of earners.