NEW YORK — Stocks tumbled Friday on escalating worries about the financial sector and rebounding oil prices. The Dow Jones industrial average sank more than 170 points. Merrill Lynch — which slashed earnings estimates for regional banks Friday — was the target of market rumors that it may issue its own profit warning. Merrill Lynch spokeswoman Jessica Oppenheim declined to comment. Merrill shares dropped $2.20, or 5.8 percent, to $35.49. The rumors added to the market’s anxiety, which ballooned Thursday when Citigroup Inc. warned of significant debt markdowns for the second quarter, Washington Mutual Inc. announced 1,200 job cuts, and Moody’s Investors Service decided late in the day to downgrade the two biggest bond insurers. For the full story visit http://www.latimes.com/business/la-fi-markets21-2008jun21,0,4358661.story