WHEN THE budget cuts already voted by Congress--and the still larger ones perhaps to come--turn into real reductions in jobs and services, how much will it strain the social fabric of the nation's communities? From Dade County, Fla., there comes a warning note.

On the front page of this paper last Saturday, Janis Johnson reported that taxpayers in the Miami area seemed, despite relatively moderate local tax rates, unwilling to pick up any of the tab for the coming large losses in federal aid. Instead they have voted to close down many basic community services. Taxpayers at a county commission hearing last week, moreover, not only were openly hostile to the society's customary scapegoats--welfare mothers, aliens and others--but were also willing to jeer down the pleas of a legless blind man who wanted help in getting to his job.

Dade County is not, of course, a typical American community, as a story in Sunday's paper also reminded us. Social relations in the Miami area were already strained to the breaking point by the influx of refugees from last year's "Freedom Flotilla," by high levels of unemployment among the area's black citizens and resistance among the English-speaking population to the demands of some of the newcomers for a thoroughly bilingual community. For these reasons Dade County's behavior cannot be taken as symptomatic of a larger trend to meanness.

Still, things can get pretty ugly in a community long before it resorts to baiting the handicapped, and there are many other areas where tax bases are strained and immigrant populations large and growing, and where unemployment is high. As the National Advisory Council on Economic Opportunity noted in its swan- song report this week, the budget cuts will surely mean fewer jobs and less help for many low-income people. The Reagan program, moreover, means not only less aid for hard-pressed communities, but also more discretion for localities, like Dade County, to call the shots on who gets what kind of help.

What happens in each community will depend, in large part, on how well the administration program succeeds in stimulating growth in local economies --some sizable defense contracts, for example, might do a lot more to ease relations in Miami than any direct government service. But the outcome will also depend importantly on the tone that is set by national and local political leaders as to what constitutes acceptable behavior toward the unfortunate in a country that is still enormously and increasingly prosperous.