LIKE MOST Americans, we thought we knew our rights. But a brand-new one came to us the other night out of the blue-or, more precisely, out of the black. The car radio had picked up "The Grand Ole Opry," beamed to us across the miles by clear-channel WSM-AM in Nashville, and suddenly the announcer was warning us that our "right" to listen to the Opry was being threatened by the FCC.

Now if the bureaucrats at the Federal Communications Commission were trying to stifle Nashville music, we would really get upset. Surely we have a right to listen to Dolly Parton and Roy Acuff; the First Amendment even protects Minnie Pearl. But do we have a right to hear them on WSM? That is the issue here. To make room for more AM stations, the FCC is considering breaking up the clear channels and cutting back the existing 25 superstations' unconntested range. Under one plan, WSM's reach would be restricted to about 100 miles. A less severe approach (which seems to have more commission support) would cut it down to about 750 miles.

The folks in Nashuille have been stirring up a letter-writing campaign to save the clears. If the Opry's vast range and audience were reduced, they claim, the program would no longer be able to attract top country-music stars for minimal fees.

That doesn't strike us as overwhelming cause for letting a few stations continue to monopolize these airwaves. The clear channels were designated, in the infant days of radio, to provide nationwide service when stations were few. Now that AM band is crowded, the allocations should be modified to make space for new competitors who want to offer locally oriented service here and there. WSM should be content with a 750-mile range. That would still let the Opry reach potential record-buyers as far away as Philadelphi, Toronto, Sioux Falls, Oklahoma city and (on a good night) Abilene. If there's enough demand beyond that, Opry could set up a network. If evangelists, political commentators and professional ballclubs can syndicate their sounds across the country, surely the Opry-which has elements of all three-can manage nicely that way too.