The Justice Department is investigating allegations of price fixing and other anticompetitive behavior on the national over-the-counter stock market. The probe follows about a dozen lawsuits filed in July that charge that some of Wall Street's largest brokers, including Merrill Lynch, Lehman Brothers and Alex Brown, have an unspoken agreement to fatten profits by charging excessive spreads on NASDAQ stocks. The effect: slightly higher prices for consumers when they buy stocks, and slightly lower prices when they sell. NASDAQ denies any price fixing, maintaining that the spread is determined by the forces of supply and demand for each stock. Pending the outcome of the suits and the Justice Department probe, you might consider seeking quotes from several dealers when buying or selling NASDAQ stocks.