America should commit to an immediate freeze in levels of carbon dioxide emissions and replace payroll taxes with levies on corporate pollution, Vice President Gore said yesterday in a speech at New York University in which he endorsed a series of far-reaching proposals to combat climate change.

Mr. Gore’s address, which lasted nearly an hour, marks a turning point in his effort to raise awareness and spur widespread change on national policies toward global warming. While he had spent months promoting a documentary film, “An Inconvenient Truth,” that spells out what Mr. Gore says is a “planetary emergency,” yesterday’s speech contained his most extensive proposals for solving the perceived crisis.

Calling for a popular movement to rise up against politicians “paralyzed in the face of a great threat,” Mr. Gore said the country needed an immediate freeze on levels of emissions of carbon dioxide that contribute to global warming, followed by sharp reductions in the future. Earlier this month, California passed a law mandating a 25% reduction by 2020, and several northeast states, including New York, have joined a pact to reduce emissions 20% by 2019.

Opponents of emissions standards say reductions should be voluntary and that regulation would be too costly for businesses and push jobs overseas. A spokeswoman for the White House Council on Environmental Quality, Kristen Hellmer, said the administration had set a national goal of an 18% reduction in carbon dioxide emissions by 2012 and was on track to meet that goal.

Mr. Gore renewed a call to replace taxes for Social Security and unemployment with pollution taxes, saying the swap would be revenue neutral.”Instead of discouraging businesses from hiring more employees, it would discourage business from producing more pollution,” he said.

The former presidential runner-up made several other proposals yesterday, including the creation of a Carbon Neutral Mortgage Association, or “Connie Mae,” that would make it cheaper to build energy efficient homes. He also suggested the development of an “electranet,” a grid modeled on the Internet that would allow individual homeowners and businesses to buy and sell surplus electricity. The grid, he said, would also provide a way to measure how much energy a home or business is using and identify ways for them to reduce wasteful use.

The nation’s leading auto companies, General Motors and Ford, should be “retooled” to require them to manufacture more electric and hybrid cars, Mr. Gore said. He also endorsed the use of ethanol, wind, and solar power to reduce America’s dependence on foreign oil.

Mr. Gore acknowledged the obstacles that his proposals face, saying they fall in a “no-man’s land” where the “maximum that seem politically feasible still falls far short of what would be effective.”

The two-term vice president’s emergence in the last year as the nation’s leading advocate for environmental change has stirred speculation that he may try again for the White House in 2008. Mr. Gore has said he is not mounting a presidential bid, but he has not ruled it out. While focused on climate change, his speech yesterday touched on a number of constituencies that would be key to a national campaign. Mr. Gore repeatedly cited the support of conservative evangelicals in addressing climate change, and he spoke of revitalizing the farm economy to reverse the loss of jobs in rural America.

“The odds are great that Al Gore isn’t running, but I think he’s trying to keep the door cracked open for a possible candidacy,” the director of the University of Virginia’s Center for Politics, Larry Sabato, said.

Mr. Sabato said Mr. Gore could be trying to keep his presidential hopes alive so that it would scare his potential opponents for the Democratic nomination into taking the issue of climate change seriously. “They still have to worry that he may run, and they might try to co-opt his issue, which is what he wants,” Mr. Sabato said.