NBC's "Meet the Press," television's longest running program, celebrates its 40th anniversary Friday amid disagreement between present and past hosts of the show over the format. Lawrence E. Spivak--who served as the show's moderator and panelist until he retired in 1975--says the formula for success was simple: "Pick an important guest, give him the full time and ask him the challenging questions. If the guest isn't worth the 27 minutes, you shouldn't have him on at all." Recently, the show began having more than one guest, and current host Chris Wallace defends the practice. "Larry (Spivak) had a great idea 40 years ago, but when he was doing the show, there was so little competition (for notable guests)."