IF PRESIDENT CARTER'S newly announced welfare reform were to become law overnight - at least as unlikely - to work in exactly the way he intends, what would be different? Well, a lot of people now living on welfare payments would be better off: A woman with three small kids in Mississippi, to take a dramatic exmaple, now getting $720 a year to live on, would get $4,200. Most recipients would be at least as well off and, with jobs, considerably better off. Some at the upper level of payments in high-paying states would get less.The burden of paying for welfare would be diminished for the states, though not eliminated. For its part, the federal government would have to pay out a few billion dollars more. A great many poor people who don't now have jobs would get them, and working people who are being paid at low to middle-low wage and salary scales would get some financial bolstering via tax credits and government payments.

Of course the proposal is not going to become law overnight or work exactly as intended. But outlining the theoretical best-case workings of the Carter plan does have this advantage: It tells us what we all mean by that increasingly mind-blocking tag "welfare reform." Principally what we mean is a more fair and orderly method of financing welfare; we do not so much mean a scheme for changing the conditions that have put one American in 10 on the receiving end of welfare benefits.

To be sure, a large part of the welfare population is composed of the blind, aged and disabled and persons otherwise unable to support themselves. And humane, decent treatment of such citizens is a minimal obligation of any civilized society. But so, we think, is an effort to release those who can be released from the dead-end bondage of welfare dependency. That is the reason we think the jobs and job-support part of Mr. Carter's program is so important. It represents a commitment to breaking into and breaking up the cycle of welfare dependency that has created a population of beneficiaries who - from one generation to the next - are systematically being drained of dignity, hope self-confidence and ambition.

In the eight years that have passed since President Nixon presented what then seemed a radical program for welfare reform, some things haven't changed at all. Here we have another new President complaining about a welfare system that is irrational and unfair in many respects and that plus a penalty on work and family stability. But some things are very much changed and for the better, we suspect - chief among them the political atmosphere. Yes, you are hearing plenty of complaints about various features of the Carter plan. But the assumptions concerning the need for a radical revision of our welfare system in the first place no longer have to be proved or even much argued. And it also seems to us that the ranks of the condescending left have diminished, those insensitive and inadvertent patronizers of the poor who fought every effort to make jobs and self-sufficiency a part of the welfare population's lives. So maybe this time around there is a better chance that a decent version of welfare reform will be enacted.

None of this is to suggest that we think Mr. Carter has found the perfect program. Aspects of it - the whole relation of his jobs program to the needs and interests of other, nonwelfare workers, for example - require careful scrutiny and no doubt some considerable alteration.And the economic assumptions on which it is based, along with its predicted outlays and savings, will require just as careful and even skeptiscal an examination. But by forcing Messrs. Califano and Marshall to wrestle with the concept of a zero-cost-increase welfare reform, he forced inspection of our current programs that simply would not have been undertaken otherwise. He also averted what would have been the most normal and predictable response to an instruction to draw up a welfare reform: a (roughly) $23 billion innovation that might not have been much better and could have been worse. We think that while there is much yet to fathom about the Carter proposal and probably a considerable amount to refine and change, the administration has done its work well: It has come out at the right place.