* Moody's changes EU rating outlook to negative
* ISM manufacturing, construction spending data on tap
* Futures down: S&P 1.4 pts, Dow 2 pts, Nasdaq 1 pt
By Angela Moon
NEW YORK, Sept 4 (Reuters) - S&P 500 index futures fell on Tuesday as investors returned after a long weekend, with focus on U.S. manufacturing data and an upcoming meeting of European Central Bank policymakers.
* Moody's Investors Service has changed its outlook on the Aaa rating of the European Union to negative, warning it might downgrade the bloc if it decides to cut the ratings on Germany, France, UK and Netherlands.
* The move will add to pressure on the European Central Bank to provide details of a new debt-buying program to help deeply indebted euro zone states at its policy meeting on Thursday.
* The Institute for Supply Management releases its August manufacturing index at 10:00 a.m. ET (1400 GMT). Economists expect a reading of 50.0, versus 49.8 in July.
* Xerox Corp and a wholly-owned unit that contracted with Texas to process dental claim forms are being investigated to see if they helped allow dentists to submit higher-than-required bills under the state's Medicaid system, the Wall Street Journal reported.
* Heckmann said it would buy privately-held environmental services firm Power Fuels for about $380.5 million in cash and shares, to expand the waste water management group's footprint in the Bakken Shale basin, an unconventional oil shale.
* The Commerce Department releases July construction spending numbers at 10:00 a.m. ET (1400 GMT). Economists forecast a rise of 0.4 percent, a repeat of the June increase.
* U.S. Secretary of State Hillary Clinton has pledged to take a strong message to Beijing this week on the need to calm regional tensions over maritime disputes that have raised broader fears of military friction between the two major Pacific powers.
* U.S. stocks rose on Friday after Federal Reserve Chairman Ben Bernanke, expressing "grave concern" for the stagnating U.S. job market, said the central bank was prepared to take further steps to strengthen the economy if necessary.
* S&P 500 futures fell 1.4 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 fell 2 points, while Nasdaq 100 futures lost 1 point.