TORONTO (Reuters) - The Toronto Stock Exchange's main index slumped more than three percent yesterday, battered by a sell-off in Research In Motion, tumbling resource shares and uncertainty over the US financial rescue plan.

Tech bellwether RIM set the tone as it skidded 28.2 percent to C$72.57 the day after the BlackBerry-maker said its profit will lag expectations as it spends money on developing a new generation of smartphones.

The heavyweight energy sector added to the pressure, sliding along with oil, which was hurt by worries over the bailout package. Among the losers, Canadian Natural Resources fell 4.3 percent to C$80.56.

Uncertainty over the fate of the $700 billion bailout proposal rounded out the negative sentiment, as did the seizure of US savings and loan Washington Mutual, the biggest bank failure in US history.

"I think it's encapsulated by one word more than anything else, and the word is 'uncertainty'," said Peter Chandler, senior vice-president of Canaccord Capital in Waterloo, Ontario.

"Markets have an incredible ability to factor in good news and factor in bad news - the thing that really unnerves markets is not knowing what the news is."

The S&P/TSX composite index closed down 420.51 points, or 3.35 percent, at 12,126 with all but two of its 10 main sectors in a downturn. On the week the index was down 6.1 percent

Financial shares fell two percent, with Canadian Imperial Bank of Commerce down 2.8 percent at C$62.18, and Bank of Montreal falling 3.8 percent to C$46.30.

Sun Life Financial Inc shed 6.1 percent to C$37.10 after it said it expected to take a third-quarter charge for its holdings in Washington Mutual, but could not yet quantify the impact.

The energy and materials sectors added to the pain, retreating 3.4 percent and 3.7 percent respectively. In the oil patch, Suncor Energy was down 4.7 percent at C$46.55, while fertiliser firm Agrium sagged 15.2 percent to C$65.90.