FAMILIES ON public assistance, like other families, sometimes mismanage their money and don't have enough at the end of the month to pay the rent. Others make a conscious decision to spend their allotment elsewhere, knowing that evictions take time and that welfare authorities will have to provide alternative shelter if worst comes to worst.

In the case of public-assistance recipients, though, the consequences of nonpayment of rent are more than personal. Youngsters, for whose protection the federal Aid to Families with Dependent Children program was established, lose their homes. The taxpayers have to pick up the often much larger bill for emergency shelter in hotels. And, most damaging in the long run, landlords increasingly unable to meet their costs abandon buildings and the stock of housing available to welfare clients is diminished.

Local officials, most prominently Mayor Ed Koch of New York -- where rental housing for the poor is fast disappearing -- have been urging Washington to authorize the payment of rents for welfare clients directly to landlords. This can be accomplished either by making the shelter payment in the form of a two-party check, which has to be endorsed by both the tenant and the landlord, or by paying the landlord directly. Federal regulations now allow such arrangements but also require a hearing before the step is taken. In many jurisdictions, this means months and months of delay during which evictions proceed.

In new regulations published for comment last week, the Department of Health and Human Services proposed two important changes in this system. First, when welfare recipients are more than two months in arrears in rent payments, a presumption is created that they are mismanaging their money and vendor payments can be initiated. This presumption can be rebutted if the tenant can show that an emergency or extraordinary reason prevented him from paying or that he is withholding rent in order to force the landlord to make repairs or meet the conditions of the lease. Second, once mismanagement has been determined, vendor payments can be instituted even before the hearing, with the goal of forestalling eviction.

Public comments on the proposed rules will be received until Jan. 15, but we already know what welfare agencies on the front line think. They like these changes because they will reduce evictions and encourage landlords to rent to their clients. Vendor payments are not instituted unless there is demonstrated trouble. They do not constitute a reduction in anyone's benefit but simply make it certain that a housing allowance will be used for its intended purpose. The new procedures are worth a try.