Both ABC and CBS are crowing that in the crucial sweeps last month, the “Today” show had its lowest viewership in eight years - and a ratings decline of about 10 percent from a year earlier. But execs at NBC aren’t hitting the panic button, and they certainly aren’t blaming Meredith Vieira, who replaced Katie Couric last fall. “Today” is still No. 1 in its time slot. And last year, the Olympics temporarily inflated all of NBC’s ratings. “If you told me, you’re going to lose Katie Couric, arguably the most influential person in the history of morning TV, and you’re not going to lose viewers, I’d sign on for that,” said one NBC suit. The overall drop reflects the fact that viewers are watching the morning shows less, and getting their news more from cable and the Web. “Compared to two years ago, we’ve doubled the gap between ‘Today’ and ‘GMA,’ ” a “Today” spokeswoman said. But a TV insider said “Today” is losing its dominance: “The show is trending in the wrong direction” - partly because Vieira is busy hosting “Who Wants to Be a Millionaire,” as well as raising three kids and taking care of her MS-stricken husband. When “GMA” anchor Diane Sawyer reported from Iran Feb. 12, “GMA” beat “Today” by 350,000 viewers.