After trading between $3,062.5 and $2,999 per tonne, London Metal Exchange three months copper finished at $3,010, down $31 from Tuesday's London close.
"The market is really struggling to go higher. Every time it goes higher, it fails," said Standard Bank analyst Robin Bhar.
"It seems to be making lower lows each day. Tomorrow we might come down to test the $2,970 level," he said. "For the moment more people are interested in liquidating any longs and....fresh shorting as well."
Bhar put resistance for copper at $3,070/80.
"The only thing holding up these metals was supply tightness and falling stocks, which was making sellers cautious because they don't want to be squeezed down the road," he added.
The Fed is expected to raise rates by a quarter percentage point to 2.5 percent in its sixth tightening since June, when it announces its decision at 1915 GMT, and also to give clues on the future outlook for monetary tightening.
The euro trimmed early gains to six-day highs of $1.3095 before trading at $1.3014/18 by 1640 GMT.
A firmer dollar puts pressure on the base metals complex, making dollar-denominated metals more expensive to investors and buyers holding other currencies.
Aluminium was at $1,823, down $19, while zinc fell $11.5 to close at $1,280.
In early trade, zinc jumped near to 7-1/4-year highs of $1,307 on technical buying.
Barclays Capital analyst Ingrid Sternby said zinc was supported by reports that Glencore would close its 90,000 tonnes a year Sardinian ISF zinc smelter.
Lead lost $6 to $927, while tin and nickel ended unchanged at $8,010 and $14,525, respectively.
Miners, which powered Tuesday's 54-point FTSE 100 index surge, were again in focus as investors anticipated strong results in the sector and mulled the prospect of sector consolidation as Xstrata aggressively pursues Australia's WMC Resources.