WASHINGTON  When experts on power grid reliability asked themselves recently how a cleaner energy future would look, seven of eight regional councils imagined how their systems would work with 10 percent wind power.

Only one, representing the southeastern United States, chose a radically different option: doubling nuclear power capacity.

Thirty years after the American nuclear industry abandoned scores of half-built plants because of soaring costs and operating problems like the Three Mile Island accident, skepticism persists over whether the technology is worth investing in.

Yet the pendulum may be swinging back. The 104 plants now running have sharply raised their output, emboldening utilities across the country to make a case for building new ones.