WHAT is the best way for Americans to help their poorest and most vulnerable neighbors?
That's the significant moral question underlying the work Congress now takes up as it seeks to revamp the nation's welfare system.
Both political parties agree that current federal welfare programs are not working well enough. Early in his term, President Clinton introduced, but then failed to push, a plan for welfare reform. Last fall, Republicans took up the cause in their ''Contract With America.'' They put forth more radical changes, including rejecting the idea that aid to the poor is an entitlement, something guaranteed to those who qualify for it regardless of good or bad economic times or the other spending needs of governm ent.
Both political parties now want to move more welfare decisions to the states. Republican governors would like the money in the form of block grants, with no strings attached. But both Republicans and Democrats in Congress, for different reasons, are wary of simply handing over revenue they have raised and trusting that states will spend it wisely.
The argument that states could provide 50 laboratories to test theories about how to solve the vexing problems of welfare has appeal. Mandating programs from Washington can mean ''one size fits all'' solutions, when local conditions and needs can vary widely.
Our view is that, while Congress should allow much more experimentation at the state level, it must demand some conditions on the money it turns over to states. These should include protection of food and other necessary aid to children, who make up two-thirds of those currently on welfare assistance. Their lives cannot be put at risk in the service of social experimentation.
One Washington mandate that some Republicans would require -- that no aid go to unwed teenage mothers -- ought not to be included. The scourge of teen pregnancy must be addressed, but, as President Clinton has said, ''We shouldn't punish children for their parents' mistakes.''
Sen. Phil Gramm (R) of Texas argues, ''You can't change this mammoth system without hurting some people.'' Perhaps not, but it is essential that we try. Secretary of Health and Human Services Secretary Donna Shalala framed the discussion more productively when she said, ''It's a debate about values, about how we take care of our children.''