* Valeant Pharma to buy Cephalon for $5.7 billion
* Trading volume could be light ahead of quarter end
* March ADP report expected to show private job gains
* Futures up: Dow 55 pts, S&P 6.7 pts, Nasdaq 15.25 pts
By Ryan Vlastelica
NEW YORK, March 29 (Reuters) - U.S. stock index futures rose on Wednesday as merger and acquisition activity lifted sentiment before data expected to show private-sector job creation.
* Gains may be limited by uncertainties over Japan's nuclear power situation and civil unrest in oil-producing regions. Trading volume has been weak, with Tuesday's the second-lowest of the year, suggesting shaky investor confidence as the quarter ends on Thursday.
* Canadian drugmaker Valeant Pharmaceuticals International made an unsolicited bid to buy Cephalon Inc for $5.7 billion.
* The bid follows AT&T Inc's recent proposed purchase of T-Mobile USA and eBay Inc's bid for GSI Commerce, signs that stocks could be viewed as cheap.
* Dow component DuPont, the chemical company, extended its $6 billion takeover bid for Denmark's Danisco by four weeks and said shareholders of 6 percent of Danisco's stock had accepted the offer.
* The ADP employment report, to be released at 8:15 a.m., is expected to show 203,000 private-sector jobs were created in March, fewer than in February. While the report doesn't have a high correlation with Friday's closely watched non-farm payrolls report by the Labor Department, a good ADP number could increase optimism about the labor market.
* S&P 500 futures rose 6.7 points and were above 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 added 55 points and Nasdaq 100 futures rose 15.25 points.
* Family Dollar Stores Inc reported second-quarter earnings that rose from the prior year and were at the high end of the company's forecast, which it recently raised..
* Tibco Software Inc fell 1 percent to $26 in light premarket trading a day after it gave a second-quarter outlook that implied slowing growth.
* Toyota Motor Corp and Honda Motor Corp took fresh steps to scale back production or reduce orders of some parts in North America after supplies were disrupted by the March 11 Japan earthquake.
Strength in energy lifted U.S. stocks on Tuesday as investors concentrated on adding to winning positions, but uncertainty kept trading volume light.
(Editing by Kenneth Barry)