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WASHINGTON (AP) -- A Senate blueprint for tackling global warming would require power plants and vehicles to reduce their greenhouse gases by 70 percent. A chief sponsor said President Bush's approach of voluntary action will not meet the goal.

The proposal Thursday by Sens. John Warner, R-Va., and Joe Lieberman, a Connecticut independent, was seen as a compromise that could get the 60 votes needed to pass, perhaps next year.

''It is the tipping point ... a breakthrough,'' said Lieberman, who heads the Senate Environmental and Public Works subcommittee that will write the legislation. Warner is the panel's top Republican.

Lawmakers already have introduced a half-dozen bills that recommend limits on greenhouse gases; some are more aggressive than the one from Lieberman and Warner. But not one has the strong bipartisan support.

In addition to Warner, Republican Sens. Elizabeth Dole of North Carolina, Norm Coleman of Minnesota and Susan Collins of Maine are co-sponsors, as is Sen. Tom Harkin, D-Iowa.

In a Senate speech, Warner acknowledged ''basic differences'' with the Bush administration. The president has opposed mandatory limits on greenhouse gases, saying such regulations would stifle economic growth.

''We feel voluntary (actions) will not achieve the goal (or) the leadership the United States of America must take on this issue,'' Warner said.

The Lieberman-Warner proposal won the endorsement of the committee chairman, Sen. Barbara Boxer, who has proposed cutting emissions by as much as 80 percent by mid-century. But Boxer, D-Calif., said the compromise bill was ''a turning point'' that ''would be the strongest global warming program in the world in terms of its reach'' if it became law.

Boxer said the proposal meets all her basic principles on dealing with climate change.

The plan would set a mandatory cap on greenhouse gases, principally carbon dioxide, from electric power, manufacturing and transportation sources. Its goal to cut annual emissions by 15 percent in 2020 and 70 percent by 2050 from 2005 levels. Carbon dioxide emissions are rising by about 1 percent a year.

Government-imposed limits would cover about three-fourths of all releases of greenhouse gases. Warner and Lieberman say other parts of the legislation could lead to further emissions cuts from sources such as private homes, which are not covered in the restrictions. Examples include new energy efficiency requirements and possibly more stringent actions that state could have permission to take.

The measure attracted broad support among environmentalists, although some said it did not go far enough and would not achieve reduction levels needed to stabilize greenhouses gases in the atmosphere to avoid the serious climate impact.

Lieberman and Warner said the reductions -- if other countries act as well -- would be enough to stabilize the gases at safe levels.

''We think it's a very strong bill,'' said Dan Lashoff, a climate expert at the Natural Resources Defense Council, a leading Washington-based environmental advocacy group closely involved in the climate debate.

Lashoff said the bill does not cover all sources of greenhouse gases. But he said it would provide incentives for states to adopt additional measures such as new building codes and energy efficiency investments that would lead to further emission reductions.

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