MOST OF the residents of Hardenburgh, N.Y., thought they had come upon a good thing in 1976. After getting themselves ordained as ministers of the Universal Life Church, 200 of the 236 received exemptions from the property tax because they were ministers.

The New York legislature -- understandably -- didn't much like this exodus from the tax rolls, particularly when it learned the Universal Life Church issues "certificates of ministry" by mail and many of the 200 Hardenburghers had been ordained in a ceremony in a cocktail lounge. But not liking it and doing something about it are two different things; distinguishing among religious beliefs is a tricky business under the First Amendment.

The legislature has succeeded, at least to the satisfaction of the New York courts, in voiding most of the tax exemptions. It did so by declaring that the only property entitled to the religious exemption from taxation is that held exclusively for church use. No doubt the decision of the New York Court of Appeals upholding the law will be appealed, and the Supreme Court will get a chance to try to start untangling what is becoming a national problem.

The Internal Revenue Service says that more than 10,000 citizens are now involved in various schemes to avoid paying federal income taxes by claiming religious exemptions. One organization, for example, has been offering (for a fee) its assistance to Washington-area residents in setting up household churches. The principal wage earner declares himself to be the minister and contributes his income to the "church," the only other members of which are his relatives. The assistance offered by the national organization includes helping establish the legitimacy of this arrangement to the satisfaction of the tax collectors.

While the New York rule appears to provide an easy way to get at property tax avoidance schemes, it runs into a little trouble when it confronts the household church concept. Can you declare your house to be a church, hold services in it for your family and meet the exemption requirement? Probably not, since that calls for "exclusive" use of a property for religious purposes. But what about those storefront churches that contain living quarters for people who are sincerely dedicated to spreading their religious beliefs?

The matter gets even more complicated when it involves income tax exemptions for contributions to religious organizations. Given the variations astute lawyers can figure out, that puts the government into the business of deciding which religious organizations are legitimate and which are not. That's a matter the courts have traditionally been leery of handling.

Sooner or later, if the mail-order ministry continues to expand, the whole problem will end up in the hands of Congress. When it does, the silver butterfly tax avoidance scheme that Congress is struggling to understand now will look simple.