TORONTO - Ontario Premier Dalton McGuinty emerged Friday as the unlikely voice of support for federal Liberal Leader Stephane Dion's carbon tax plan, which he once dismissed in favour of a cap-and-trade system with neighbouring Quebec.

McGuinty, who twice vetoed the idea of a carbon tax in his province, said he "likes the sound" of the plan Dion unveiled Thursday following weeks of attacks by the governing Conservatives.

"I like the fact that Mr. Dion is putting a real price on pollution and then he throws in the added benefit of reducing income taxes and guarantees revenue neutrality through an independent third party," he said.

"I like the sound of all that stuff."

McGuinty, whose brother David serves as environment critic for the federal Liberals, was singing a different tune last month when he said his "first choice" for Ontario was an interprovincial carbon trading system with Quebec.

The Liberal premier also rejected the idea in February, after British Columbia unveiled a carbon tax in its provincial budget.

But Dion may have had time to convince McGuinty of the plan's merits when he met with the premier last weekend during the Ontario Liberals' annual meeting in Ottawa.

When asked Friday about his change of heart, McGuinty suggested the two strategies to cut down on harmful greenhouse gas emissions were not necessarily mutually exclusive.

"The choice coming up in the federal election is not my approach (versus) Mr. Dion's approach. I'm not running," he said.

"It's Mr. Dion's approach and other approaches put forward by federal parties."

Several provincial leaders have rejected Dion's "green shift" plan, while others have been reluctant to embrace it.

The carbon tax would raise about $15.4 billion a year, but would be offset by an equivalent cut in income and business taxes and a boost in tax breaks for poor, elderly, northern and rural Canadians who stand to be hardest hit by the increased cost of necessities like home heating fuel, electricity, food and travel.

Speaking in Saskatoon, Prime Minister Stephen Harper warned the proposal would prove as disastrous as the old national energy program, a Liberal proposal which is still criticized for draining money from the West - especially Alberta - and sending it to Central Canada.

"(The carbon tax plan) is like the national energy program in the sense that the national energy program was designed to screw the West and really damage the energy sector - and this will do those things," Harper said.

"This is different in that this will actually screw everybody across the country."