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* Boeing falls after reporting $3 bln Q2 loss
* Caterpillar slips on lower quarterly earnings
* Big Tech faces broad Justice Department antitrust probe
* Futures down: Dow 0.34%, S&P 0.20%, Nasdaq 0.33% (Adds comment, updates prices)
By Amy Caren Daniel
July 24 (Reuters) - U.S. stock market futures fell on Wednesday after bleak earnings from bellwethers Caterpillar and Boeing added to the concerns over a slowing economy that have weighed heavily on sentiment this year.
Caterpillar Inc, whose exposure to China has made it an important measure of the global impact of trade tensions, dropped 4.7% after it reported a fall in quarterly earnings and cooling demand for construction machines in Asia.
The world's largest planemaker matched that with a well-flagged slump in results on the back of this year's groundings of its best-selling 737 MAX planes after two deadly crashes.
Two weeks into the guts of an earnings season for which investors have already dialed down expectations, the manufacturing firms' results came on the same day as a grim set of forward-looking surveys on the euro zone economy.
"Caterpillar's results show that there is weakness in the Asia Pacific region, and if there is a slowdown there, where is the next pocket of slowdown, and people could start extrapolating from that," Andre Bakhos, managing director at New Vines Capital LLC in Bernardsville, New Jersey
"Caterpillar's earnings are more important than Boeing, because Boeing's issues are more company specific."
Nearly 80% of the 104 S&P 500 companies to report so far have topped earnings expectations, and overall profits are expected to rise about 1%, according to Refinitiv, improving from a small decline estimated previously.
Sentiment, however, remains shaky and other corporate newsflow, including the announcement of a broad antitrust investigation by the U.S. Justice Department into the tech sector, fed into the losses.
The DOJ did not identify specific companies, but the terms of the review pointed to Alphabet Inc, Amazon.com Inc and Facebook Inc and shares in all three fell about 1%.
Facebook reports its own earnings later on Wednesday and it was also the subject of a pair of settlements announced by regulators on privacy issues that included fines of more than $5 billion, again well-flagged previously.
At 8:38 a.m. ET, Dow e-minis were down 92 points, or 0.34%. S&P 500 e-minis were down 6 points, or 0.2% and Nasdaq 100 e-minis were down 26.5 points, or 0.33%. (Reporting by Amy Caren Daniel in Bengaluru; editing by Patrick Graham)