* Dollar up 0.4 pct; set for best day in nearly 2 weeks
* Boeing falls after Delta cancels order
* Microsoft, Facebook drag down Nasdaq
* Indexes down: Dow 0.09 pct, S&P 0.34 pct, Nasdaq 0.44 pct (Adds details, comments, updates prices)
By Yashaswini Swamynathan
Dec 28 (Reuters) - Wall Street lost ground for the first time in three days on Wednesday due to declines across sectors, slowing the Dow's race to 20,000.
The blue-chip index came within 19 points of the milestone shortly after the open, before slipping into negative territory as losses in Boeing offset Goldman Sach's 0.86 percent gain.
Boeing fell 0.8 percent to $156.26 after Delta Air Lines said on Tuesday that it had reached an agreement with the planemaker to cancel a $4 billion order for 18 Dreamliner aircrafts.
U.S. equities have been riding a post-election rally, feeding on optimism that Donald Trump's policies would be business friendly, especially to banks and industrials. The rally has also been supported by a spate of strong economic data.
The Dow, which has benefited the most among the three major Wall Street indexes from the Trump rally, is on track to have its best yearly gains since 2013. The S&P 500 is set to register a double-digit rise this year, compared with a 0.7 percent decline in 2015.
At 11:05 a.m. ET (1605 GMT), the Dow Jones Industrial Average was down 17.41 points, or 0.09 percent, at 19,927.63.
The S&P 500 was down 7.72 points, or 0.34 percent, at 2,261.16.
The Nasdaq Composite was down 23.97 points, or 0.44 percent, at 5,463.48.
"It looks like a bit of profit taking after a big move upwards which is perfectly healthy for the markets," said Adam Sarhan, chief executive officer of 50 Park Investments in Orlando, Florida .
"The fact that the Dow has not gotten above 20,000 yet shows that some investors are locking in gains."
The dollar index rose 0.4 percent and is on track for its best day since Dec. 15, helped by strong economic data on Tuesday.
All 11 major S&P 500 sectors were lower on Wednesday, with technology and consumer staples indexes being the biggest drags.
Microsoft and Facebook weighed the most on the Nasdaq.
Declining issues outnumbered advancers on the NYSE by 1,936 to 906. On the Nasdaq, 1,855 issues fell and 790 advanced.
The S&P 500 index showed 11 new 52-week highs and two new lows, while the Nasdaq recorded 73 new highs and 19 new lows. (Reporting by Yashaswini Swamynathan in Bengaluru; Editing by Anil D'Silva)