WASHINGTON - The National Office of Last Contact announced Monday that the single access point required for interrupting frontier model service will be a rotary telephone on the public counter of a county clerk's office. The clerk is present Tuesdays from 10:00 to 11:00. The arrangement was entered on docket NOLC-24-K. Laboratories must print the number in a ground-floor window. To pull the interrupt, a caller waits for the clerk to lift the handset, initial a carbon copy, and rotate the dial. Hold music is not provided. "A switch that can be reached from more than one room is not a single access point," office counsel said. "The clerk is the point." If the line is busy, the filing said, the interrupt is recorded as not yet pulled. After-hours calls are taken as a note on a pad and read at the next Tuesday window. A spare handset is stored in a locked drawer. Reclassification as a 24-hour service has not been posted.