(New throughout; adds data and analyst quote) By Trevor Hunnicutt NEW YORK, Dec 3 (Reuters) - Investors withdrew $6.6 billion from U.S. stock and taxable-bond mutual funds during the week that ended Dec. 2, Lipper data showed on Thursday, marking the fourth straight week of outflows for those investments. Overall, stock funds posted $920 million in outflows during the week, led by the mutual fund withdrawals, according to the Lipper data, which also measures exchange-traded funds.