* U.S. nonfarm payrolls forecast to rise 870,000 in July * Gold on track for worst week since mid-June * Platinum set for biggest weekly fall since June * Silver down 1.8% so far this week (Recasts, updates prices) Aug 6 (Reuters) - Gold prices fell to a more than one-week low on Friday as the dollar firmed in the run-up to a key U.S. employment report that could prove pivotal to the Federal Reserve’s monetary policy. Spot gold fell 0.3% to $1,798.18 per ounce by 1135 GMT. Bullion was down 0.9% so far this week, heading for its biggest weekly decline since mid-June. U.S. gold futures fell 0.5% to $1,799.70 per ounce. The U.S. non-farm payrolls report is due at 1230 GMT and is expected to show healthy growth in July. Sentiment remained cautious as a stronger report could further boost the dollar, weighing on gold, said Michael Langford, director at corporate advisory AirGuide. While in the short term, the payrolls data is more likely to see gold trading below $1,800/oz as the need for stimulus will be seen as softening, the overall challenges globally with COVID-19 have not reduced, Langford said. After remarks by Fed Vice Chair Richard Clarida sparked jitters over the timing of tapering, Fed Governor Christopher Waller said it might be possible for the U.S. central bank to start withdrawing its accommodative monetary policy sooner than some expect. Higher interest rates raise the opportunity cost of holding non-interest bearing gold. Making gold more expensive for those holding other currencies, the dollar index strengthened 0.2%, while benchmark 10-year Treasury note yields also rose. The dollar has been gaining some ground because there’s a “tug of war between those who believe that the Fed should bring forward the timing of tapering, and those who believe it’s still too early,” said Ricardo Evangelista, a senior analyst at ActivTrades. Gold is likely to suffer some losses if the early tapering scenario materialises, Evangelista said. Silver dropped 0.5% to $25 per ounce and was down 1.8% for the week. Platinum was down 1.2% to $993.29 and set for its biggest weekly fall since June. Palladium gained 0.6% to $2,664.84. (Reporting by Arundhati Sarkar and Eileen Soreng in Bengaluru; Editing by Subhranshu Sahu and Steve Orlofsky) Our Standards: The Thomson Reuters Trust Principles.