In providing his strongest indication yet that he might look to nuclear energy to meet Ontario's long-term electricity supply concerns, McGuinty said he's prepared to agree on construction of multibillion-dollar nuclear plants if that's what it takes to quench the province's increasing thirst for energy.

The premier said he's awaiting a Dec. 1 report from the newly created Ontario Power Authority, which is reviewing what needs to be done to address concerns about the province's energy supply.

"Should the OPA recommend nuclear as being an indispensable part of a diverse supply of electricity, then we will build new nuclear in this province," McGuinty said.

McGuinty was speaking from Niagara Falls, where he attended a ground-breaking ceremony for Ontario Power Generation's construction of a 10-kilometre tunnel. The tunnel will divert more hydroelectric power from the waters around Canada's honeymoon capital to a power station further up the Niagara River.

The premier said it's an example of how the government is addressing concerns about the energy supply in the short-term, especially in light of extreme heat in Ontario this summer.

But he said that over the longer term, larger projects will be needed, even if it means expanding the use of controversial nuclear energy.

Proponents of nuclear power say it's the cleanest and safest way to add significant power to the province's electricity system.

Critics say nuclear plants cost billions of dollars to construct, take 10 years or more to build and raise environmental concerns about radioactive waste.

The Toronto Environmental Alliance said it was "appalled" to hear McGuinty open the door to more nuclear plants, which it warned would leave a huge financial and environmental debt.

"We're very concerned because the (electricity) system is still very much in the hands of the people who built our last nuclear plants, and got us into the mess we're in today," said alliance spokesman Keith Stewart.

"The McGuinty government should not be repeating the mistakes of the previous provincial government, which put us massively in debt, and left us with nuclear plants that don't work very well and we're all paying for right now."

Even after the OPA report is completed, Energy Minister Dwight Duncan noted that months of review will be necessary before the province gives the go-ahead to any nuclear projects.

"There are going to be a series of other questions after (the report is released), starting with private versus public, starting with OPG's role, and then doing all the calculations and arithmetic around what projects would and wouldn't be feasible," Duncan said.

The Conservatives and New Democrats said McGuinty is taking too long to make up his mind on an energy strategy two years into his mandate.

"They don't seem to have a plan for replacing the generation that they've committed to shutting down," Tory energy critic John Yakabuski said, referring to the premier's promise to close coal- fired plants, which has been delayed.

Yakabuski said Ontario manufacturers won't invest more in the province until they're sure the energy supply is reliable.

NDP Leader Howard Hampton said the province should look to ways of encouraging better energy conservation.

Hampton estimated a new nuclear plant could cost as much as $10 billion to construct and noted that the Darlington nuclear plant cost nearly three times as much to build than originally anticipated.

"We can get further with energy efficiency . . . it will be cheaper than building $10-billion nuclear plants."

At a speech to the Ontario Energy Association in Niagara Falls, McGuinty said he's willing to take a political hit for building nuclear plants even if they prove unpopular. He accused previous governments of having delayed dealing with the nuclear issue.

"We won't gamble away Ontario's future prosperity because of what the next poll might or might not say," he told industry officials.

Murray Elston, president of the Canadian Nuclear Association, said costs to build a nuclear plant can be kept under control as long as there's a firm commitment to construct them, an no starts and stops.

"The one thing which is absolutely key for our industry is that once the decision is taken that we get on with putting the projects in the ground," Elston said.