Current fashion in social theory holds that welfare and other programs to help the poor are self-defeating. Far from curing poverty, so the argument goes, welfare spending has only exacerbated it by corrupting low-income people into permanent dependence.

This line of thinking naturally falls on receptive ears. How much more comforting to be able to justify a lack of generosity by concern for -- rather than indifference to -- those in need of help. ("God knows, we wish we could do more to help them, but it would be cruel to try.")

Realize, moreover, that this -- rather than the activist social policy of the last two decades -- has been the dominant strain in Anglo-American thinking about the poor. For centuries the British were tormented by fear that the generosity of the Poor Laws would be abused by the meaner classes. Such concern prompted authorities to cut the food ration in workhouses and poor farms in the early part of the 19th century and to require that fathers be separated from their families as a condition of public aid. As Charles Dickens observed in "Oliver Twist," the ration cut produced a gratifying reduction in the number of dependent poor -- not because they became more self-supporting, but because many obligingly passed on to a presumably better world, leaving the taxpayer with only the cost of a pauper's burial -- not insignificant but at least nonrecurring.

Currently the leading exponent of the justified-neglect approach is a pleasant-mannered researcher named Charles Murray. In his book, "Losing Ground," Murray argues that the growth of spending on social programs over the past 20 years has arrested progress against poverty. Because of its allegedly corrosive effect on the poor, Murray recommends stping all welfare help to the able-bodied -- Aid to Families with Dependent Children (AFDC), food stamps and medical aid. So intuitively appealing is this thesis that few critics have noticed that the facts tend to contradict rather than support his argument.

In the first place, in recent years welfare spending on the able-bodied poor -- the only group Murray says he is concerned about -- has not spiraled. AFDC benefits, which are set by states, have lost 40 percent of their purchasing power since 1970 -- and they weren't very generous then. Food stamps have made up only part of that loss. The big growth has been in social insurance programs -- Social Security and Medicare -- that don't reach working-age families. Even Medicaid spends most of its money on the elderly and long-term disabled.

Moreover, during the period when welfare spending for families was increasing, poverty among this group declined. In fact, poverty among families dropped considerably faster from 1964 to 1969 than in the preceding 17 years, a trend that doesn't show up in Murray's charts because the poverty data he cites aren't consistent between the two periods.

One reason why dire poverty dropped in the late 1960s was that welfare participation grew very rapidly. And, as many careful studies have documented and as Murray acknowledges, welfare caseloads swelled not because more generous programs bred more eligible families, but because increased outreach efforts brought many desperately poor people onto the rolls. In other words, the programs worked.

By the early 1970s almost all eligible families were receiving benefits and -- contrary to popular belief and political rhetoric -- caseloads stopped growing. Since 1972 the number of families receiving AFDC benefits has simply bobbed up and down with the business cycle.

That leveling off is all the more remarkable since the group most likely to go on welfare -- young women -- grew rapidly during the 1970s as the baby boom generation reached maturity. This was also a period of slow economic growth and rapidly changing attitudes toward sexual behavior -- two factors that could be expected to increase the numbers of husbandless mothers dependent on welfare. But child-bearing among all race and age groups including teen-agers -- the group most likely to end up on welfare -- continued to decline from peak levels of the late 1950s.

True, more of those births -- especially to black teen-agers -- were likely to occur out of wedlock, and that is a social problem well worth worrying about. But, as a recent study by Harvard researchers David Ellwood and Mary Jo Bane carefully documents, there is no evidence that the level of welfare benefits has any effect on the number of single mothers. This finding is further supported by the fact that, over the last two decades, the number of non-poor fatherless families grew faster than the number of such families in poverty. If welfare were the main cause -- or even a very important cause -- of the creation of female-headed families, then you would surely expect those eligible for welfare to increase more rapidly than those that aren't -- and that hasn't been the case.

Finally, it's worth noting that, just as poverty among families declined when welfare grew during the late 1960s, so, as welfare has been cut back especially sharply in the last three years, the number of parents and children in poverty has climbed.

Although Murray's basic thesis doesn't hold up, his book is a useful reminder to policy makers that intended good deeds can have unfortunate side effects. If you ask very little of students, most of them won't learn very much. If penalties for criminal behavior are lenient or rarely applied, more crime will be committed. If financial and psychic returns from work are small or nonexistent, people will tend to work less. If young people have no hope for a better future, a life on welfare may not seem intolerably bleak.

Few people ever doubted that incentives of this sort affect behavior, but the social programmers of the 1960s and 1970s sometimes forgot about that in their enthusiasm. The central issue, however, is not whether programs have unintended side effects but whether these side effects are serious enough to undermine the basis for the programs.

Side effects of programs for the relatively well-off -- tax subsidies, farm price supports, water projects and so on -- are rarely considered important enough to justify their abolition. Never mind, for example, that far too much U.S. investment flows into housing at the expense of other sectors.

The idea of abolishing tax benefits for real estate ownership and development is politically unthinkable, even though the housing industry would surely survive, albeit in leaner form. Curiously, however, it appears to be at least thinkable that the society should deprive poor families of the most basic sustenance lest they be corrupted by kindness.