THE BEST that can be said for the mayor's veto of the rent-increase bill is that it cancelled what was no more than a quick fix for the rental-housing crisis. Whether this will turn out to have been the right move will depend entirely on what use the city council makes of the time it bought when it followed up the veto with a 90-day extension of the existing rent-control legislation. Almost nobody thinks the present system works, and nobody seriously believed that the rent increases were anything more than a stop-gap measure to alleviate some of the worst consequences of an unworkable system. Moreover, a case can be made that a rent increases might have indefinitely delayed a serious effort to overhaul rent controls as they are now applied. So there could be a bright side to the veto and to the 90-day extension if - and it is a very tentative if - the opportunity is now seized for a serious effort to deal with the inequities and malfunctions of the existing program before the present extension expires on Jan. 31.

As we see it, there are only three choices. The council could allow the extension to lapse and eliminate rent control altogether - a proposition that is as unwise as it is unlikely to be carried out. Doing away with rent control in an abrupt manner would create chaos in the city's rental market. A second choice would be to extend the existing legislation. That notion may be appealing to the council, especially in view of the political heat that will be generated by next year's election. But a desite to extend the legislation as to avoid making hard choices is hardly justification for perpetuating an already unworkable system.

The best choice would be for the council to get quickly to the hard work of revising the whole system. The emphasis should be on untangling the continuing administrative mess. Some way must be found to get at the backlog of landlord appeals and resolve them. What this would require is an immediate review of present cases and a new procedure to cut down on necessary paperwork and inordinate delays. It would help if luxury-housing units were removed from rent-control system altogether. It is also clear that some type of rent increases - along with appropriate safeguards for tenants - is sorely needed. unless the council takes these and other defects of the present system into account, there will almost certainly be a decline in maintenance and management services, and landlords will most likely give greater thought to selling or abandoning their properties, thereby increasing the shortage of rental units. The council can ignore these prospects only at the peril of seeing the crisis in the rental-housing market grow steadily worse.