* Potential capital gains tax cuts eyed by investors
* Twitter falls after CTO announces departure
* Accenture lower after forecast misses estimates
* Indexes down: Dow 0.04 pct, S&P 0.09 pct, Nasdaq 0.07 pct (Updates to afternoon)
By Noel Randewich
Dec 21 (Reuters) - U.S. stocks were largely unchanged on Wednesday, with energy stocks slightly stronger and healthcare down a little, a day after the Nasdaq Composite and the Dow Jones Industrial Average hit record highs.
The Dow briefly rose to within 15 points of 20,000, the historic level it has threatened to breach for several days, but it relinquished that gain.
U.S. stocks have rallied since the Nov. 8 election, with the Dow up about 9 percent and the S&P 500 6 percent on bets that President-elect Donald Trump's plans for deregulation and infrastructure spending will boost the economy.
Some investors are concerned that the so-called "Trump rally" has made stocks expensive. The S&P 500 is trading at about 17 times expected 12-month earnings, well above the 10-year average of 14, according to Thomson Reuters Datastream.
"People are taking a pause and they want to see what's going to happen," said Chris Zaccarelli, Chief Investment Officer for Cornerstone Financial Partners. "In his first 100 days in office, it will be interesting to see what legislation they can get through Congress and what regulations they will repeal."
Providing the market with support this week, expectations of lower capital gains tax rates under Trump are giving investors an incentive to not sell stocks until January, according to Zaccarelli as well as to Randy Frederick, Vice President of Trading & Derivatives at Charles Schwab.
"If you can hold back on capital gains for two weeks, why not?," Frederick said. "There's just no incentive to sell right now."
At 2:22 pm ET, the Dow Jones Industrial Average was down 0.04 percent at 19,965.91 points and the S&P 500 had lost 0.09 percent to 2,268.66.
The Nasdaq Composite edged down 0.07 percent to 5,480.15.
The S&P energy sector added 0.39 percent, while the healthcare sector dipped 0.41 percent.
Accenture fell 5 percent after the consulting and outsourcing software services provider's revenue forecast missed estimates. The stock was the biggest drag on the S&P.
Twitter fell 4.21 percent after its chief technology officer said he would be leaving the company.
FedEx fell 2.83 percent after the package delivery company's quarterly results missed expectations.
Advancing issues outnumbered declining ones on the NYSE by a 1.13-to-1 ratio; on Nasdaq, a 1.23-to-1 ratio favored decliners.
The S&P 500 posted 21 new 52-week highs and 1 new lows; the Nasdaq Composite recorded 164 new highs and 34 new lows. (Additional reporting by Tanya Agrawal in Bengaluru; Editing by Chizu Nomiyama)