Households with incomes of less than $600 a month get 68.2 percent of their money from government payments consisting mainly of Social Security and welfare, the Census Bureau reported yesterday.

In contrast, the richest households -- those that take in $5,000 a month or more -- get only 2.5 percent of their income from government.

The report, detailing where Americans get their money, illustrates the deep dependence of the nation's poorest families on the comprehensive income-support programs that were started in the New Deal period.

It helps explain why relatively small cuts in government programs can effect large reductions in the income of the poor.

The report shows that for the nation as a whole, all income groups receive $77.50 of every $100 of income from jobs, $10.70 from Social Security and various government payments, $7.70 from interest, rents and dividends, and the rest from private pensions and charity.

But the pattern is sharply different for both the lowest and highest income groups.

Overall, the report shows, 12.4 million of the nation's 84 million households have less than $600 a month in income, and only 20.4 percent of the money comes from jobs. Only 2.6 million of these households get any income from earnings.

Social Security makes up the single largest source of money income for the under $600-a-month group, accounting for 43.2 percent. Aid to Families with Dependent Children and related cash aid is next, accounting for 14.1 percent of income for the group and Supplemental Security Income (welfare for the aged, blind and disabled) is third at 7.7 percent. Veterans', private, military and government employe pensions account for most of the remainder, and property income the rest.

These figures indicate that at least three-quarters of the households with the lowest incomes consist of elderly and disabled retirees living on pensions and of welfare families which have dependent children.

Families in the next income category, containing 15.5 million households, make between $600 and $1,200 a month. They also depend heavily on government payments, although 48.8 percent of their income comes from work. This group gets 35 percent of its income from government payments, with Social Security, at 27.8 percent of all income, by far the largest contributor.

At the other end of the income scale -- the 5.5 million households making $5,000 a month or more -- the picture is quite different, with 80 percent of income coming from jobs, 14.3 percent from interest, dividends and rent, and 2.5 percent from government payments. Although the households in this income group made up only 6.5 percent of all households, they had a quarter of all income.

The lowest-income group made up a seventh of all households but had only about a fiftieth of all cash income.

The survey also showed that more than half the nation's blacks were in households receiving cash or non-cash welfare benefits of some type. Two-fifths of the Hispanics but only about one-seventh of the whites were in such households.