After trading in positive territory for most of Tuesday's session, stocks sold off late in the afternoon to end firmly in the red and near their lows for the day. The NYSE composite dropped 0.9%, the S&P 500 0.6% and the Nasdaq 0.3%. Volume increased from Monday's levels on both main exchanges, adding vehemence to the move lower. All three indexes touched their lowest levels in the past three to four months. Also discouraging: The Nasdaq and S&P