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* WH adviser warns govt shutdown could lead to zero Q1 GDP growth
* CEOs at Davos express loss of confidence in Trump trade policies
* Dow pulled higher by upbeat earnings from IBM, PG, UTX
* Dow up 0.53 pct, S&P flat, Nasdaq down 0.18 pct (Updates to late afternoon, changes dateline, byline)
By Stephen Culp
Jan 23 (Reuters) - Wall Street struggled for direction on Wednesday, as early gains driven by a spate of upbeat earnings were offset by concerns about a potential economic downturn, trade tensions and longest government shutdown in U.S. history.
While the S&P 500 was flat and the Nasdaq edged lower, the blue chip Dow Jones Industrial Average rose as positive quarterly results from International Business Machines, Procter & Gamble Co, United Technologies and others helped pull the index into positive territory.
Optimism early in the session was dampened by reports that business leaders gathered at the World Economic Forum in Davos, Switzerland, were losing confidence in President Donald Trump's policies as the effects from the prolonged U.S.-China trade stand-off become more deeply felt.
Uncertainty persisted in Washington, where no end to the longest-ever federal government shutdown appeared to be in sight.
The United States could see zero growth in the first quarter if the shutdown extends through March, according to White House economic adviser Kevin Hassett on Wednesday.
"It relates to the weakness yesterday, people being unsure, a market that's gotten overbought over a short amount of time," said Robert Pavlik, chief investment strategist, senior portfolio manager at SlateStone Wealth LLC in New York.
"A lot of people are questioning the government shutdown, and with CEOs saying they're concerned about the trade policies, this speaks to the same underlying issue that people aren't sure what's going to happen with the global economy," Pavlik added.
Still, a spate of positive earnings kept the Dow in the black.
International Business Machines Corp provided the biggest boost to the Dow, rising 8.7 percent after cloud and software services helped its profit come in above analyst estimates and the company offered better-than-expected guidance for 2019.
Procter & Gamble rose 4.0 percent after the company upped its full-year sales forecast and took advantage of price increases and strong demand to beat analyst earnings estimates.
United Technologies reported a better-than-expected fourth-quarter profit and forecast 2019 earnings above analyst estimates. The industrial conglomerate's stock was up 5.0 percent.
The Dow Jones Industrial Average rose 129.28 points, or 0.53 percent, to 24,533.76, the S&P 500 gained 0.64 point, or 0.02 percent, to 2,633.54 and the Nasdaq Composite dropped 12.80 points, or 0.18 percent, to 7,007.55.
Fourth-quarter reporting season is in full-swing, and of the 15 percent of S&P 500 companies that have reported, 77.6 percent have beaten analststs' estimates, according to Refinitiv data.
Analysts now see S&P 500 earnings growth of 14.2 percent in the quarter.
Comcast Corp rose 4.5 percent after the top U.S. cable service provider posted better-than-expected earnings and announced it would raise its dividend by 10 percent.
Kimberly-Clark Corp's quarterly profit fell short of expectations as the consumer products company struggled with rising raw materials costs and the strong U.S. dollar. Its shares slipped 2.7 percent.
Shares of Tesla Inc dropped 4.6 percent after the electric automaker said it was reducing production hours for higher-priced Model S and Model X cars, days after announcing job cuts.
Ford Motor Co is expected to announce results after markets close today.
Declining issues outnumbered advancing ones on the NYSE by a 1.17-to-1 ratio; on Nasdaq, a 1.20-to-1 ratio favored decliners.
The S&P 500 posted four new 52-week highs and one new lows; the Nasdaq Composite recorded 16 new highs and 39 new lows.
Reporting by Stephen Culp; Editing by Steve Orlofsky