The top 1 percent of earners in the United States saw their average household incomes grow a whopping 279 percent from 1979 to 2007, according to a Congressional Budget Office (CBO) study (PDF) published this week.

For the lowest earners, what the CBO described as the poorest fifth of America, average incomes grew just 18 percent in that same period. The middle class -- comprised of about three-fifths of Americans -- saw incomes grow about 40 percent.

Those figures should be enough to enrage virtually all of the 99 Percent protesters demonstrating in nearly every major U.S. city for the last month, who see themselves as being the forgotten segment of society and wish to highlight the nation's growing income disparity.

All told, the gap between rich and poor in America more than tripled in just under 30 years, marching in line with government policies that have increasingly tended to rely on regressive taxes on the poor and working classes, and less on taxing the top earners.

That's led to a massive imbalance and an increasing rate of growth for the wealthiest Americans, who saw their incomes swell more than 17 percent of all total earnings in 2007 alone. The lowest one-fifth of earners, however, claimed just 5 percent of income that same year.

The study's figures, pieced together from market research, census data and Internal Revenue Service (IRS) statistics, essentially confirms what other groups have been saying (PDF) in recent years: the gap between rich and poor in the U.S. is at the greatest it has ever been, and shows no signs of slowing its growth.

Right now in Washington, support is growing, albeit slowly, for higher tax rates on the wealthiest Americans: something that the vast majority of U.S. voters want to see. Republicans in Congress, however, have put up a unified opposition to the president's plans, and many Democrats in the Senate have joined them.

Unlike partisan think tanks raising alarms over America's growing income disparity, the CBO's report is likely to give significant weight to liberals who want to see wealthy Americans and corporations paying tax rates that are more in line with the percentage of incomes contributed by the poor and working classes.

Whether it will be enough to cause action by a Congress that has been hallmarked by dogged inaction remains to be seen.

Photo: Flickr user aka Kath.