The 400 highest-earning U.S. households reported an average of $345 million in income in 2007, up 31 percent from a year earlier, IRS statistics show. The average tax rate for the households fell to the lowest in almost 20 years. The figures for 2007, the last year of an economic expansion, show that the average income reported by the top 400 earners more than doubled from $131.1 million in 2001. That year, Congress adopted tax cuts urged by then-President George W. Bush that Democrats say disproportionately benefit the wealthy. Each household in the top 400 of earners paid an average tax rate of 16.6 percent, the lowest since the agency began tracking the data in 1992. The statistics underscore two long-term trends: that income at the very top has exploded and their taxes have been cut dramatically," said Chuck Marr, director of federal tax policy at the Center on Budget and Policy Priorities, a Washington-based research group that supports increasing taxes on high-income individuals. The top 400 earners received a total $138 billion in 2007, up from $105.3 billion a year earlier. On an inflation-adjusted basis, their average income grew almost fivefold since 1992.