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* Wall St drops despite Trump's tweet that Phase 1 deal on Jan. 15
* Consumer confidence slips in December
* S&P 500 set for best year since 2013
* Indexes fall: Dow 0.19%, S&P 0.16%, Nasdaq 0.02% (Adds comment; updates prices)
By Manas Mishra
Dec 31 (Reuters) - Wall Street dipped in thin trading on the last day of the decade as a year-end rally powered by optimism around trade and an improving global outlook fizzled out, though the S&P 500 was still on course for its best year since 2013.
The Dow Jones was on track for its second straight day of declines, shrugging off President Donald Trump's tweet that a Phase 1 U.S-China trade deal would be signed on Jan. 15 at the White House, and that he would later travel to Beijing to begin negotiations on the next phase.
"It's getting to the point where I feel like Phase 1 is becoming more and more priced in," said Keith Buchanan, portfolio manager at GLOBALT in Atlanta.
A relatively loose monetary policy by the Federal Reserve and upbeat economic indicators have put the S&P 500 on track for its best December in nine years.
The three major indexes posted their biggest one-day declines in about four weeks on Monday, in the absence of major updates on trade, and as investors booked profits.
"With Phase 1 looking to be in the rear view mirror in the earlier part of January, we could go back to the same place where we are trying to figure out where things go from here as we look at a Phase 2 deal," Buchanan added.
On Tuesday, eight of the 11 S&P 500 sectors were in the red, with healthcare among the top drags.
Schlumberger NV and Baker Hughes Co were among the top percentage decliners on the S&P, tracking lower oil prices.
At 12:11 p.m. ET, the Dow Jones Industrial Average was down 54.89 points, or 0.19%, at 28,407.25, the S&P 500 was down 5.29 points, or 0.16%, at 3,216.00. The Nasdaq Composite was down 1.75 points, or 0.02%, at 8,944.24.
Data showed a reading of the U.S. consumer confidence index was 126.5 in December, compared with a revised 126.8 in November.
Among sparse individual movers, U.S.-listed shares of Tencent Music Entertainment Group rose 1.4% after a consortium led by the China-based company agreed to buy a stake in Vivendi's Universal Music Group.
Advancing issues outnumbered decliners for a 1.45-to-1 ratio on the NYSE and a 1.53-to-1 ratio on the Nasdaq.
The S&P index recorded three new 52-week highs and no new low, while the Nasdaq recorded 62 new highs and 17 new lows. (Reporting by Manas Mishra in Bengaluru; Editing by Anil D'Silva, Maju Samuel and Shounak Dasgupta)