* Crude oil falls after last week's gains
* Tyco soars after deal to merge with Johnson Controls
* Twitter falls as 4 top executives to leave co
* Indexes down: Dow 0.64 pct, S&P 0.79 pct, Nasdaq 0.55 pct (Adds details, changes comment, updates prices)
By Abhiram Nandakumar
Jan 25 (Reuters) - Wall Street looked set to snap a two-day rally on Monday as retreating crude oil prices weighed on materials and energy stocks.
Crude prices resumed their slide, after a strong two-day run, as a record output from Iraq flooded a heavily oversupplied market.
U.S. stocks logged their first week of gains in the year last week, with the three indexes closing up 2 percent on Friday.
Investors, already rattled by the volatile start to the year and a steep fall in oil prices, are awaiting U.S. GDP data on Friday for a reading on the health of the economy.
All eyes will be on the U.S. Federal Reserve's next move on interest rates when the Federal Open Market Committee meets on Jan. 26-27.
"As much as we'd like things to change and we have a new calendar, the same themes are playing out today and this week," said Eric Wiegand, senior portfolio manager at the Private Client Reserve at U.S. Bank in New York.
"Clearly, the fervor around selling had largely hit a peak. Last week, I don't think there was a sense that it was all clear, or a resounding sense of confidence that perhaps the lows have been put in," Wiegand said.
Corporate results are not likely to improve sentiment, with quarterly profits at S&P 500 companies expected to fall 4.5 percent, according to Thomson Reuters data. Excluding energy companies, earnings are estimated to grow by 1.6 percent.
At 11:02 a.m. ET (1602 GMT), the Dow Jones industrial average was down 102.48 points, or 0.64 percent, at 15,991.03, the S&P 500 was down 14.99 points, or 0.79 percent, at 1,891.91 and the Nasdaq Composite index was down 25.16 points, or 0.55 percent, at 4,566.02.
Nine of the 10 major S&P sectors were lower, led by the 1.95 percent fall in the materials sector. Monsanto weighed the most on the sector.
Packaging company Westrock was down 11.6 percent at $33.36 and International Paper was down 6.7 percent at $34.04 after Citigroup and Jefferies cut ratings on both stocks.
Exxon and Chevron were off about 1 percent, while Conocophillips was down 5.6 percent at $35.55 after Barclays said the oil and natural gas producer should cut its dividend by 75 percent.
Shares of Caterpillar were down 3.8 percent at $58.65 after Goldman Sachs cut its rating on the stock to "sell". The stock was the biggest drag on the Dow.
McDonald's was up 1.6 percent at $120.31 after the Dow component reported better-than-expected same-store sales.
Tyco International jumped 7.2 percent to $32.76 after Johnson Controls said it would merge with the Irish fire protection and security systems maker. Johnson Controls was down 3.6 percent at $34.33.
Twitter was down 4.3 percent at $17.07 after Chief Executive Jack Dorsey said four senior executives would leave the social media company.
Declining issues outnumbered advancing ones on the NYSE by 2,247 to 664. On the Nasdaq, 1,679 issues fell and 931 advanced.
The S&P 500 index showed 3 new 52-week highs and 13 new lows, while the Nasdaq recorded 8 new highs and 42 new lows. (Reporting by Abhiram Nandakumar in Bengaluru; Editing by Anil D'Silva)