* ADP employment tops expectations
* Express tumbles after earnings, outlook
* OmniVision slumps after revenue forecast
* Futures down: Dow 19 pts, S&P 3.4 pts, Nasdaq 4.75 pts
By Chuck Mikolajczak
NEW YORK, Dec 4 (Reuters) - U.S. stocks were poised for a lower open on Wednesday, after a strong reading on private payrolls bolstered investors' expectations that the U.S. Federal Reserve will wind down its massive stimulus earlier than expected.
The benchmark S&P 500 has fallen for the three past sessions, putting the index on track to snap an eight-week winning streak during which it added nearly 7 percent, partly on concerns of an imminent wind-down of Fed stimulus.
Many market participants expect the Fed to announce a cut to its $85 billion in monthly bond purchases in March, but recent economic data has suggested the move may come even sooner.
Adding fuel to those expectations was a rosy ADP National Employment Report released early Wednesday, which showed private employers added 215,000 jobs in November, topping economists' expectations of 173,000 jobs, with the prior month revised upward by 54,000 jobs.
Also, the U.S. trade deficit narrowed to $40.6 billion in October as exports hit a record high, slightly less than the $40.0 billion expectation of economists but still pointing to a pick-up in global demand that should help to support domestic growth in the fourth quarter.
The Fed has said it would slow its stimulus program when certain economic measures meet its targets, including an improvement in the labor market.
"Today it's all going to be about the ADP number, the trade deficit is not going to matter too much," said Mike Serio, regional chief investment officer for Wells Fargo Private Bank in Denver, Colorado.
"In the short term the market is still worried about the most inevitable thing in our lifetime and that is tapering."
S&P 500 futures fell 3.4 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures lost 19 points and Nasdaq 100 futures declined 4.75 points.
Shares of clothing retailer Express Inc tumbled 18.9 percent to $20 in premarket trading after the company forecast quarterly earnings would be below analysts' estimates due to weaker-than-expected Thanksgiving sales.
OmniVision Technologies Inc slumped 12.1 percent to $14.06 before the opening bell after the chipmaker forecast current-quarter revenue well below analysts' estimates.
Oculus Innovative Sciences Inc shares surged 161.9 percent to $6.09 in premarket trading after receiving the go-ahead from the U.S. Food and Drug Administration for its anti-scar gel.
More data is due later in the day.
At 10:00 a.m. (1500 GMT), the Institute for Supply Management releases its November non-manufacturing index and the Commerce Department releases new home sales for September and October. Economists surveyed by Reuters forecast an ISM services reading of 55.0 versus 55.4 in October. New home sales for September are forecast to show a total of 425,000 annualized units and 428,000 for October.
Later at 2:00 p.m. (1900 GMT), the Federal Reserve will release its Beige Book of regional economic conditions.