Cable television shows and their stars will be eligible for prime-time Emmy Award consideration beginning next year, the Academy of Television Arts and Sciences has announced. The decision follows eight years of debate on the issue, once vigorously opposed by the networks. The rule-change means such series as "It's Garry Shandling's Show," the widely praised Showtime offering, now may compete with network favorites in the comedy category. Programs available to more than 50% of American TV homes qualify for consideration, meaning all but a handful of smaller channels could be included in the balloting. The TV academy will publish a list of eligible cable channels shortly before the nominating process begins, a spokesman said.