* TSX down 20.10 points, or 0.16 percent, at 12,790.11 * Seven of 10 main index sectors decline * Materials group down 1.4 percent as commodity prices slip By John Tilak TORONTO, Feb 20 (Reuters) - Canada's main stock index fell on Wednesday with weak commodity prices weighing on resource shares as the market awaited release of minutes from the most recent U.S. Federal Reserve meeting, looking for clues on the state of the world's largest economy. Investors also tracked data that showed groundbreakings for U.S. homes fell in January but new permits for construction rose to a 4-1/2-year high, reinforcing expectations the housing market will support economic growth this year. The minutes from the Federal Open Market Committee meeting, to be released later in the day, were expected to offer hints on any Fed plans to modify its loose monetary policy due to changes in economic conditions. "Investors are fairly confident that the worst is over, that we are going to have an economic recovery, but it's going to be substandard," said Ian Nakamoto, director of research at MacDougall, MacDougall & MacTier. The Toronto Stock Exchange's S&P/TSX composite index was down 20.10 points, or 0.16 percent, at 12,790.11 at midmorning on Wednesday. Seven of the index's 10 main sectors were in the red. The materials sector, which includes mining stocks, slipped 1.4 percent. Gold and silver prices fell to six-month lows ahead of the Fed meeting. "The question is whether they (commodity prices) are going to bottom and start moving up," Nakamoto said. He expects them to rise in the second half of this year. The biggest decliners on the index were the miners. Silver Wheaton Corp dropped 3.7 percent to C$33.71. Yamana Gold Inc was down 3.4 percent at C$14.71, and Goldcorp Inc fell 1.3 percent to C$33.60. The energy sector fell 0.1 percent as oil prices declined. Financials, the index's weightiest sector, were up 0.4 percent. Bank of Nova Scotia gained 1.2 percent to C$59.88, and Toronto-Dominion Bank rose 0.6 percent to C$84.36.