TORONTO (Reuters) - The Toronto Stock Exchange's main index ended sharply lower for a third straight session, as resource issues fell on weakness in commodity prices, while BCE also weighed.The S&P/TSX composite index closed down 177.98 points, or 1.29 percent, at 13,663.88. The benchmark index has shed more than 430 points over the past three sessions.

"We're fairing worse than the Dow and the Nasdaq simply because we're more sensitive to oil and gas, and the mining sector," said Irwin Michael, portfolio manager at ABC Funds.

"Not terribly great volumes but it seems like a little bit of a buyer's boycott," he added.

All but one of the TSX index's 10 main groups were lower, led by a 1.9 percent slide in the heavyweight energy sector and a 2.3 percent retreat in the materials index. The health care sector was up 0.1 percent.

Energy issues, which make up about 30 percent of the market's weight, fell as US crude oil retreated C$1.41, or two percent, to $67.77 a barrel due to expectations of rising U.S. inventories.

EnCana dropped C$1.96, or 2.9 percent, to C$65.38, while Suncor Energy dove C$2.17, or 2.3 percent, to C$92.63.

EnCana is the operator of the proposed Deep Panuke offshore gas project in Nova Scotia. Exxon Mobil and Royal Dutch Shell want to sell their combined 18 percent stake in the C$700 million project, the broker handling the auction said yesterday.

Zinc giant Teck Cominco was off C$1.33, or 2.9 percent, at C$45.30, while Barrick Gold fell 86 Canadian cents, or 2.8 percent, to C$30.08.

"Currently, I think it's sort of a combination of profit-taking and interest rate fears," said Michael Sprung, president of Sprung & Co. Investment Counsel.

"Our view is that, finally, people are beginning to get very concerned. We've had some bad consumer confidence data and housing data persisting from the US, all the problems with the subprime lending program."

News swirling around BCE didn't help the market today, either, Sprung added.

Telecom shares, down 1.5 percent, as BCE dropped C$1.23, or three percent, to C$39.49, after rival Telus said it was backing out of the bidding process to take over BCE.

Telus rose 19 Canadian cents, or 0.3 percent, to C$62.19.

"The market wouldn't take that as being positive to see the potential bidders leaving the table," said Sprung.