* Apple drops after disappointing sales, profit margin forecast
* Boeing loses premarket gains to trade 0.4 pct lower
* Biogen's strong profit beat lifts shares
* Indexes down: Dow 0.54 pct, S&P 0.48 pct, Nasdaq 0.55 pct (Updates to open)
By Yashaswini Swamynathan
Oct 26 (Reuters) - Wall Street was lower on Wednesday morning as Apple's weak results weighed on technology stocks and oil prices fell amid worries of oversupply.
Shares of the world's most valuable public company fell 3.7 percent - set for their worst day in six months - after the company said sales of its flagship iPhones fell for the third quarter in a row.
Apple was the top drag on all three major indexes. The S&P 500 technology index fell 0.72 percent, the biggest decline among the 10 sectors under pressure.
Oil prices fell more than 2 percent - Brent crude was on track for the fourth day of declines - after Iraq said it did not want to join an output-limiting deal with OPEC members, and U.S. drillers stepped up work.
Movement on Wall Street has largely been dictated by corporate earnings in the past few weeks, but events such as the Nov. 8 U.S. presidential election and the Federal Reserve's policy meet next week have added volatility.
Overall earnings of S&P 500 companies are expected to rise 1.8 percent, snapping a four-quarter streak of profit declines, according to Thomson Reuters I/B/E/S.
Excluding Apple, earnings are expected to rise 2.5 percent.
"The earnings season on balance has been much better than expected, said Art Hogan, chief market strategist at Wunderlich Equity Capital Markets.
"But the glaring difference this quarter is that companies which meet or beat expectations get rewarded modestly while those that miss are seeing a more severe reaction."
At 9:33 a.m. ET (1333 GMT), the Dow Jones Industrial Average was down 97.66 points, or 0.54 percent, at 18,071.61.
The S&P 500 was down 10.29 points, or 0.48 percent, at 2,132.87 and the Nasdaq Composite was down 29.00 points, or 0.55 percent, at 5,254.40.
Shares of Dow component Boeing was down 0.44 percent after the company reported results.
Biogen rose 2.7 percent to $293.38 after the drugmaker reported a rise in quarterly profit that blew past estimates.
Chipotle Mexican Grill dropped 5 percent after the restaurant chain operator reported a bigger-than-expected drop in quarterly sales at established restaurants.
Edwards Lifesciences plunged 14 percent after the medical device maker reported third-quarter sales that missed expectations.
Declining issues outnumbered advancing ones on the NYSE by 2,035 to 498. On the Nasdaq, 1,508 issues fell and 525 advanced.
The S&P 500 index showed two new 52-week highs and three new lows, while the Nasdaq recorded 12 new highs and 28 new lows. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Don Sebastian)