* Pfizer falls after abandoning plan to split
* U.S. presidential debate kicks off at 9:00 p.m. ET
* Deutsche Bank down, weighs on U.S. financials
* Indexes down: Dow 0.56 pct, S&P 0.46 pct, Nasdaq 0.61 pct (Adds details, comments, updates prices)
By Yashaswini Swamynathan
Sept 26 (Reuters) - Wall Street was lower late Monday morning, dragged down by Pfizer and as investors anxiously await the first U.S. presidential debate to gauge how the candidates plan to shape the economy and policy.
Pfizer fell 1.6 percent after it decided against splitting into two. The stock was the biggest drag on the S&P 500 healthcare index, which fell 0.98 percent, making it the biggest loser among the nine declining S&P sectors.
While the White House race has so far had little discernible effect on the market, that may soon change as polls show a tightening race ahead of the first debate between Hillary Clinton and Donald Trump.
With just over six weeks until Election Day, some investors see a toss-up contest creating volatility in certain sectors, including health insurers, drugmakers and industrials.
"Investors are acting extremely nervous with regards to the debate ... and it highlights the fact that the markets are not focusing on the health of the economy, interest rates and geopolitical events," said Robert Pavlik, chief market strategist at Boston Private Wealth.
The CBOE Market Volatility index, also known as Wall Street's "fear gauge", was up 1.5 percent, clocking its biggest percentage gain in nearly two weeks.
At 10:55 a.m. ET (1455 GMT), the Dow Jones Industrial Average was down 103.14 points, or 0.56 percent, at 18,158.31.
The S&P 500 was down 9.99 points, or 0.46 percent, at 2,154.7.
The Nasdaq Composite was down 32.32 points, or 0.61 percent, at 5,273.43.
Adding to investors' unease was Deutsche Bank's U.S.-listed stock touching a record low and dragging big Wall Street banks, after a German magazine said Chancellor Angela Merkel has ruled out state assistance for the lender.
The bank said it had no need for German government help with a $14 billion U.S. demand to settle claims it missold mortgage-backed securities.
The S&P financial index fell 0.7 percent. Goldman Sachs' was the top drag on the Dow, while JPMorgan dropped 1 percent.
Oil prices rallied 3.6 percent as the world's largest producers gathered in Algeria to potentially work out a plan to limit output.
The energy index's 0.78 percent gain was the most among the 11 major S&P sectors.
Declining issues outnumbered advancing ones on the NYSE by 1,766 to 1,104. On the Nasdaq, 1,805 issues fell and 792 advanced.
The S&P 500 index showed two new 52-week highs and one new lows, while the Nasdaq recorded 31 new highs and 17 new lows. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Saumyadeb Chakrabarty and Savio D'Souza)