Nearly half the nation's elderly would be living below the poverty line without Social Security and other government payments, a Census Bureau study scheduled for release Wednesday showed.

The experimental study, which was obtained late Tuesday, measured the effects of taxes and government transfer payments on income inequality.The report found that poverty would be deeper, especially for the elderly, and the rich would control more of the nation's wealth without taxes and government assistance, including food stamps, school lunches, rent subsidies, Medicare and Medicaid.

"The large differences measure the importance of Social Security income to the elderly," the report said.

Figures for 1986 show that total national household income - defined as money income before taxes excluding capital gains - totaled $2.7 trillion with a median household income of $24,897. The bottom 20 percent of those households received only 3.8 percent of the total income while the top 20 percent garnered 46.1 percent.

The proportion of people living in poverty was 13.6 percent.

When the Census Bureau excluded government payments but added in employment-provided health benefits, aggregate income rose to $2.87 trillion and median household income was $24,211. But using this method, the lowest 20 percent of households shared only 1 percent of the nation's wealth while the upper 20 percent controlled 54.4 percent. The poverty rate was 19.9 percent.

For the elderly, the contrast was even more stark. Using the second definition of income that excludes government payments, households with one or more persons older than 65 had a median income of only $7,005. The poverty rate was 47 percent.

Under the first income definition, which includes government payments, median household income was $14,922 in 1986 and the poverty rate fell to 12.4 percent.