(Adds details on market activity throughout; updates prices)
By Fergal Smith
TORONTO, March 7 (Reuters) - Canada's main stock index fell on Wednesday as a drop in commodity prices weighed on resource shares, while steel producer Stelco Holdings Inc rallied on prospects for Canada to be exempted from proposed U.S. metals tariffs.
* The White House said Canada and Mexico, and possibly other countries, may be exempted from planned U.S. import tariffs on steel and aluminum on the basis of national security.
* Stelco rose 3.9 percent to C$24.63. The stock had hit a nearly seven-week low on Tuesday at C$23.00.
* The Toronto Stock Exchange's S&P/TSX composite index closed down 72.58 points, or 0.47 percent, at 15,472.61.
* The resignation of Gary Cohn, top economic adviser to U.S. President Donald Trump, intensified investor worries over a global trade war, while the Bank of Canada said trade policy is an "important and growing source of uncertainty."
* The materials group, which includes precious and base metals miners and fertilizer companies, lost 1.4 percent.
* Agnico Eagle Mines Ltd fell 2.0 percent to C$49.47 after Credit Suisse cut its price target on the stock.
* Gold futures fell 0.2 percent to $1,326 an ounce, while U.S. crude oil futures settled 2.3 percent lower at $61.15 a barrel.
* The energy group fell nearly 1 percent, with TransCanada Corp down 2.3 percent at C$55.65.
* The shares of trade-sensitive auto parts and railroad companies lost ground. Magna International Inc declined 0.4 percent to C$67.66 and Canadian National Railway Co was down 0.7 percent at C$94.09.
* Great Canadian Gaming Corp rose 12.4 percent to C$38.15 after reporting fourth-quarter results after the bell on Tuesday. (Reporting by Fergal Smith Editing by Bernadette Baum and James Dalgleish)