OTTAWA - Conservative support has been eroding in a vital Ontario battleground targeted by Tories, Liberals and New Democrats alike, a new poll suggests.

The Canadian Press Harris-Decima survey indicates the lead the Conservatives enjoyed in the 905 area code of southern Ontario during the last campaign has vanished and the Liberals enjoy a substantial edge in the region.

The Conservatives, the Liberals and the NDP have focused the majority of their resources on a handful of truly competitive ridings across the country. The 905 horseshoe of suburban ridings around Toronto stretching down to Niagara Falls are among the most hotly contested.

"That's an absolutely critical region of this country for any political party," said Jeff Walker, Harris-Decima senior vice-president. "No part of the country is probably as critical to winning or losing an election than 905."

In the final Harris-Decima poll before the last election, the Conservatives held a strong lead in the region. That has now turned right around.

"What's happening in 905 right now is quite incredible," said Walker.

Coupled with a Conservative decline in support in Quebec that started during the last election and has continued, the findings for southern Ontario bode badly for the Tories, Walker said.

"The fact that they're hurting so badly in Quebec is a problem, but the fact that they're behind as much as they are in 905 is arguably as big a problem."

The poll contacted just over 2,000 people between May 28 and June 8 as part of an omnibus phone survey. It is considered accurate to within 2.2 percentage points, 19 times out of 20.

On a national basis, voter intentions give the Liberals 35 per cent, the Conservatives 31, the NDP 15, the Bloc nine and the Greens eight.

Across Ontario the Liberals lead the Conservatives 42-31. The NDP has 14 per cent and the Greens have 11 per cent. There is a 3.8 per cent margin of error in the provincial numbers.

In Toronto itself and around the curve of eastern curve of Lake Ontario, the Liberal lead is even more pronounced.

In the 416 area code in Toronto itself, the Liberals have the support of 52 per cent of respondents, while the Conservatives and NDP are tied at 19 per cent. The margin of error for this sample is eight per cent.

In the 905 region, the Liberal lead is 50-27, with the NDP at 11 per cent. The margin of error in this data is 7.8 per cent. Before the last election, the Tories led 44-32 here.

Walker said the Conservatives will have to reverse this slump they are to have a shot at winning re-election.

"I would say that 905 is the critical bellwether for suburban Canada and the Conservatives absolutely have to win suburban Canada if they want to win the next election

He said all is not bleak for the Tories, despite the numbers and the downward trend.

"The good news for them is that they're still holding on around 30 (per cent) overall," he said.

This is in spite of the recession, rising unemployment and political gaffes such as the Lisa Raitt story.

"They're still holding at 30. It's not the end of the world."

He said Tory efforts to improve their fortunes haven't budged voters so far. Their attack adds aimed at Liberal Leader Michael Ignatieff aren't doing anything to shift voting intentions, even though almost two thirds of poll respondents say they've seen the ads.

"So far, not much of what they've been doing has been working for them," Walker said.

But the Conservatives may have the luxury of time.

Walker said the data from the 416 area code suggests the NDP is tied with the Tories in support.

"With those splits it means the NDP has very little chance of winning more than one or two ridings in 416," he said. "The NDP has absolutely no incentive to go to an election right now."

Since it will take the combined votes of all three opposition parties to topple the government and force an election, that may give the Harper government an extended lease.