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* Facebook, Twitter down as executives face U.S. Congress
* Deadline for consultations on U.S.-China tariffs looms
* Energy stocks drop as oil prices slip
* Halliburton down on Q3 warnings, weighs on Schlumberger
* Indexes: Dow up 0.02 pct; S&P down 0.17 pct, Nasdaq 0.42 pct (Updates to open)
Sept 5 (Reuters) - U.S. stock indexes were lower on Wednesday, weighed down by Facebook, energy stocks and concerns over the possibility of President Donald Trump going through with plans to slap new tariffs on Chinese goods as early as this week.
Facebook dipped 0.6 percent, while Twitter dropped 2.4 percent as their top executives appeared in front of the Congress over what lawmakers see as a failure to combat continuing foreign efforts to influence U.S. politics.
Facebook Chief Operating Officer Sheryl Sandberg and Twitter Chief Executive Officer Jack Dorsey started their testimony from 9:30 a.m. ET (1330 GMT) onwards. Snapchat-parent Snap Inc was down 2.5 percent.
"We are definitely going to see a negative tilt today with the big social media leaders appearing in front of Congress," said Scott Brown, chief economist at Raymond James in St. Petersburg, Florida.
U.S. trade deficit rose to a five-month high in July due to weak exports of soybeans and civilian aircraft, Commerce Department data showed, suggesting the Trump administration's protectionist policy was so far not having an impact.
The data comes as consultations on a U.S. proposal to impose tariffs on $200 billion more in Chinese imports ends on Sept. 6, with Trump ready to impose these tariffs after that, according to Bloomberg.
Caterpillar and Boeing were down 0.4 percent each.
The United States and Canada will also resume talks to settle differences on revamping the North American Free Trade Agreement (NAFTA), despite Trump's threats to continue trade deals with just Mexico in a bilateral agreement.
"There's still a cloud hanging over the market about whether we are actually going to see these (Chinese) tariffs take effect by the end of this week and continued concerns about the NAFTA deal," said Brown.
Nine of the 11 major S&P sectors were lower, led by a 0.92 percent drop in energy stocks.
Oil fell below $78 a barrel as a U.S. Gulf tropical storm weakened and moved away from oil-producing areas and concern about weakening global demand added downward pressure.
At 9:56 a.m. ET the Dow Jones Industrial Average was up 4.81 points, or 0.02 percent, at 25,957.29, the S&P 500 was down 4.82 points, or 0.17 percent, at 2,891.90 and the Nasdaq Composite was down 34.28 points, or 0.42 percent, at 8,056.97.
Halliburton dropped 5.6 percent, the most on the S&P, after the oilfield services provider said it expects moderating oil and gas activity in North America and a slower-than-expected ramp up of new contracts in the Middle East to hurt third-quarter results.
Shares of rival Schlumberger fell 1.6 percent on the news.
General Electric, whose oilfield services arm is Baker Hughes, was down 2.4 percent. Brokerage UBS cut its price target on GE's stock on concerns over the company's power business.
JD.com declined 6.5 percent, down for the second day in a row, after police said the Chinese retailer's chief executive officer was arrested in Minneapolis last week following an allegation of rape. CEO Richard Liu has denied any wrongdoing and was released on Saturday.
Declining issues outnumbered advancers for a 1.89-to-1 ratio on the NYSE and a 1.99-to-1 ratio on the Nasdaq.
The S&P index recorded 28 new 52-week highs and six new lows, while the Nasdaq recorded 47 new highs and 16 new lows. (Reporting by Shreyashi Sanyal in Bengaluru; Editing by Shounak Dasgupta)