After Black Friday's strong gains on light volume, investors focused on the delayed international help for Greece and worries that lawmakers in Washington would not be able to intervene in time to stop the "fiscal cliff."
The fiscal cliff is a series of federal spending cuts and tax increases totaling half a trillion dollars that, absent a bipartisan agreement, become law Jan. 1.
By close of trading, the Dow Jones industrial average dropped 42.31 points or 0.33 percent to 12,967.37.
The Nasdaq added 9.93 points or 0.33 percent to 2,976.78 and the Standard & Poor's 500 lost 2.86 points or 0.2 percent to 1,406.29.
On the New York Stock Exchange, 1,323 stocks advanced and 1,726 declined on a volume of 2.9 billion shares traded.
The 10-year treasury note rose 8/32 to yield 1.667 percent.
On currency markets, the euro rose to $1.2992 from Friday's $1.2975. The dollar fell to 82.06 yen from Friday's 82.40 yen.
Japan's Nikkei rose 1.8 percent, 166.42 points, to 9,388.94 while the Hong Kong Hang Seng index was up 0.55 percent to 21,861.81, a gain of 118.61 points.
In London, the FTSE 100 index shed 0.56 percent, 32.42, to 5,786.72.
The DAX 30 in Germany lost 0.23 percent, 17.10, to 7,292.03.