NEW YORK, Sept 9 (Reuters) - U.S. stock index futures are flat on Tuesday, with investors finding few reasons to buy following a long-running rally that has taken indexes to repeated records, although market valuations are seen as able to support further gains.
* Markets have been struggling for direction of late, with daily moves small and trading volume recently among the lowest of the year. While some of the low volume can be credited to seasonal issues and the recent Labor Day holiday, which closed markets for a day last week, it also indicates that investors are reluctant to jump in at current levels.
* The S&P 500's price-to-earnings ratio is 16, a level that is well within historical averages, suggesting that prices are not unduly stretched at current levels.
* The benchmark index briefly fell under its 14-day moving average on Monday, though it was able to recover and end above the level, which is viewed as a key indicator of short-term momentum. A close under the moving average, which is currently 1996.92, could signal further losses ahead. The S&P has not had a correction - defined as a 10 percent decline from a market peak - since 2012.
* Crude oil is up 0.7 percent, indicating a modest rebound after three straight days of declines. Energy shares have recently weighed on the market, including in Monday's session, as a stronger dollar pressured the commodity and energy-related stocks.
Futures snapshot at 6:38:
* S&P 500 e-minis remained unchanged, with 85,259 contracts changing hands.
* Nasdaq 100 e-minis are gaining 2.75 points, or 0.07 percent, in volume of 16,300 contracts.
* Dow e-minis are up 6 points, or 0.04 percent, with 17,753 contracts changing hands. (Editing by Lisa Von Ahn)