By 2030, the number of residents in New York City could put such a strain on its infrastructure that the demand for power exceeds the supply, housing becomes scarce and rush hour lasts all day because of an overwhelmed transit network.

Mayor Michael Bloomberg and a panel of experts warned Tuesday that this city of 8.2 million people must start planning and building for the expected population growth of another million over the next 25 years.

"We now have the freedom to take on the obstacles looming in the city's future and to begin clearing them away before they become rooted in place," Bloomberg said.

A team of city planners, academics, scientists and environmentalists have spent the past year studying the city's infrastructure and assessing its viability for years to come. Some of them were assembled Tuesday to discuss their findings and begin mapping out possible solutions.

The conclusions were bleak:

— Energy demand could exceed supply by as soon as 2012, and by 2030 the majority of the city's power plants will be more than 50 years old. The city needs to improve efficiency, use alternative energy sources and modernize its grid, which was built during the 1920s.

— In 25 years, rails and roadways will be "crammed beyond capacity" and won't be able to accommodate the swarm of commuters in the normal rush hour, the group predicts. Lawmakers must act now to not only expand the roadway network but also to update the subway, which was built starting in 1901 and still uses signal and switch technology developed before the 1940s.

— The city will need to accommodate its booming population with thousands more units of housing. And it has to be affordable — already, more than a third of city renters fork over more than half their income toward rent, the group said.

Robert D. Yaro, president of the Regional Plan Association, a nonpartisan planning group, said New York must not only meet the needs of its growing population but has to stay competitive as a global city.

"We gotta get ahead of the trend," he said. "We can't put our head in the sand. We know that Shanghai and London and other great world cities that are competing with us are making plans like these and are doing a great job of building new economies and building the infrastructure systems."

The group noted that planners who created the street grid plan in 1811 had the sense to plot out room for a population 10 times what it was at the time. And in the 1850s, leaders already had the vision to carve out a vast Central Park, even though much of the city was still farmland and open fields.

"Previous generations imagined how New York would change, and they delivered," Bloomberg said. "And now it's our turn."

Yaro cautioned that the city will have to proceed carefully with development to preserve the character and uniqueness essential to its neighborhoods.

Development projects in the city can be tricky. Bloomberg's plan for a new football stadium and conference center on Manhattan's West Side failed miserably last year, and other complexes in that area and swaths of Brooklyn have run up against powerful opposition from residents and other concerned groups.

The Bloomberg administration is not yet offering policies to magically solve the problems of the future, but the mayor said Tuesday that the city is launching a campaign for public input, with the hopes of finding creative answers.

Suggestions offered by the expert panel included taxing vehicles that drive into Manhattan's most heavily trafficked neighborhoods, called congestion pricing, and charging residents by the pound for the trash they throw out.

Bloomberg didn't rule out anything.

"Every good idea will be on the table ... every reasonable proposal will get a fair hearing," he said.