* Wall St reverses gains from regular trading session
* Investors to turn focus to "fiscal cliff"
* Futures off: S&P 6.7 pts, Dow 50 pts, Nasdaq 8.75 pts
NEW YORK, Nov 7 (Reuters) - U.S. stock index futures fell late on Tuesday, but were off session lows, as major TV networks called the U.S. presidential election for Democratic incumbent Barack Obama over challenger Mitt Romney.
S&P 500 futures fell 6.7 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration of the contract. Dow Jones industrial average futures lost 50 points and Nasdaq 100 futures fell 8.75 points.
S&P futures earlier fell as much as 14 points.
Cash markets posted strong gains earlier despite a string of weaker-than expected results from U.S. companies, with notable strength in stocks and sectors that were seen favorable under a Romney win, including coal, energy and defense shares.
"The first reaction is a giveback of today's movement, but the fact that we'll have a decision is as important as anything," said Art Hogan, managing director at Lazard Capital Markets in New York.
He said the most important market catalyst now is the speed at which Washington deals with the so-called fiscal cliff, some $600 billion in spending cuts and tax increases that are due to kick in next year and could derail the U.S. economic recovery.
The vote including congressional races points to a status quo result, Democrats retaining control of the Senate and the House of Representatives staying in Republican hands.