Sen. Daniel Patrick Moynihan is leading another of those periodic rituals in which rich people cry about the cost of supporting the children of poor people.

Amid calls for ''welfare reform,'' ''work fare'' and efforts to force people to support the children they produce, Moynihan has come up with something called the Child Support Supplement, which is supposed to replace the much-maligned welfare program called Aid to Families With Dependent Children.

Look at the Census Bureau's recent report on poverty and income in America in 1986, and you'll see why neither Moynihan's nor anyone else's scheme is likely to change much.

That report shows that the rich are getting richer and the poor are finding deeper poverty. The poorest 20 percent of Americans got 4.1 percent of the money in 1970, but only 3.8 percent in 1986. The richest 20 percent got 46.1 percent of the money, up from 43.3 percent in 1970. Even the middle 60 percent saw their share of the money decline from 52.7 percent to 50.2 percent.

The richer the rich get, the more they complain about the cost of supporting the poor. The complaints about welfare for children become easier when the affluent see which children are on welfare. For every 100 black children under 6, 45.6 percent live in poverty; for every 100 Hispanics under 6, 40.7 percent are impoverished, and for every 100 white children under 6, 17.7 percent live in poverty.

There was considerable boasting by Reagan administration officials that economic recovery had caused the total number of Americans in poverty to drop from 33.1 million in 1985 to 32.4 million in 1986. But in terms of the welfare problem, those figures are relatively meaningless compared with the fact that the number of impoverished female-headed families rose by 139,000 to 3.6 million. ''It appears that female heads of household are more difficult to reach through economic growth and job creation, especially when they have family responsibilities and children at home,'' said Census Bureau official Gordon W. Green Jr.

Divorce and desertion have become so commonplace in America, the stigma against having babies out of wedlock so weak, that the likelihood is that the number of female-headed households will continue to rise.

Simply as a matter of public policy, this raises the question of whether the federal government should oppose abortion counseling and abortion availability, thus practically decreeing that the poorest girls and women in the land will produce babies for whom neither they nor the fathers can provide.

It is a hollow gesture to pass a law demanding work fare and responsibility from irresponsible youngsters whose preparation for work is limited, and whose neighborhoods offer little family-supporting labor.

My love for the work ethic is such that I'd rejoice to see every parent laboring to support his or her children. But I know that this is not always possible or socially wise, given the paucity of jobs in poor neighborhoods, the lack of affordable transportation to areas where work is available, the lack of child-care facilities.

The challenge is for us to make better training available to the children of the poor; to find ways to keep more of them in school; to ensure that jobs are available after school. We can even dream about lowering the rates of divorce and desertion.

But the way we run our society today guarantees that the poor will always be with us, with a compelling need for help from that 20 percent of Americans who get 46 percent of the money.