* TSX ends down 14.92 points, or 0.12 percent, at 12,388.71 * Index weighed down by miners hurt by falling bullion price * Bombardier gains after Latvian order By Alastair Sharp TORONTO, Dec 20 (Reuters) - Canada's main stock index fell on Thursday, as miners retreated in the face of sharp drops in the price of gold and other metals and hurt by uncertainty over stalled U.S. budget discussions. Bullion fell to its lowest price since August, while silver and platinum also retreated as heavy liquidation of positions and signs of an improving U.S. economy triggered a technical sell-off. The U.S. economy - Canada's largest trading partner - grew faster than previously thought in the third quarter but a sluggish world economy and belt-tightening by Washington looks set to put on the brakes again. Adding to the negative tone, Republicans in the U.S. House of Representatives pushed ahead with their own "fiscal cliff" plan on Thursday, mu ddyi ng n egotiations with the White House to avoid steep tax increases and spending cuts th at could push the country back into recession. [I D:nL1E8NK3JM] "It's a pretty tired market," said John Stephenson, senior vice president at First Asset Investment Management. "The market wants to go higher but there is all this uncertainty regarding the fiscal cliff." The Toronto Stock Exchange's S&P/TSX composite index e nded d own 1 4. 9 2 points, or 0.1 2 percent, at 12,38 8.7 1 . Four of the 10 main sectors ended lower , with the materials sector, which includes gold miners, leading the declines. B y contrast, U.S. indices ended in positive territory. Miner Goldcorp Inc finished down 2. 1 percent at C$35.17 , w hile smaller Yamana Gold fell 2.4 percent to C$16.39 a nd Silver Wheaton Corp lost 1. 4 p ercent to C$34.39 . Investors are also concerned about the fragility of the global economy, said Michael Sprung, president of Sprung Investment Management. "The markets are at levels anticipating an improving economy, although not a very robust economy," he said, adding that gold stocks could be in for another wild ride next year. "By late next year, we should see some modest recovery (in the materials sector) as I would expect China could be working inventory down and be back in the market again," he said. Energy shares slipped 0.4 percent, with U.S crude oil prices edging higher and Brent sliding. Shares of Bombardier Inc gained 3.1 percent to C$3.68 after the Canadian aircraft and train maker said Latvia's airBaltic has placed a firm order for 10 C-Series jets. First Asset's Stephenson said the dips in some resource stocks present b uying opportunities, adding that he likes pr ospects for Canadian Natural Resources Ltd <C NQ.TO>, Suncor En ergy Inc <SU .TO> an d Teck Resources Ltd<TC Kb.TO> an d that First Quantum Min erals Ltd look s attractive below $20.