* Abbot to buy Solvay's drugs unit for $6.6 billion
* Xerox will acquire ACS in a $6.4 billion deal
NEW YORK, Sept 28 (Reuters) - U.S. stock index futures rose slightly on Monday after three days of losses on Wall Street as more mergers and the last days of the third quarter encouraged investors into equities.
* Abbott Laboratories said it would buy the drugs unit of Solvay in a $6.6 billion deal giving Abbott full control of its Belgian development partner's cholesterol treatments and exposure to emerging markets.
* Xerox Corp will buy Affiliated Computer Services assume ACS's $2 billion in debt in a $6.4 billion cash and stock deal.
* "We're getting back into the routine of weekly (merger and acquisition) announcements, which is positive going forward," said Peter Cardillo, chief market economist at Avalon Partners in New York.
* "Over the next couple of days we might see some window dressing. There's still a lot of money out there," Cardillo said, referring to the expected asset repositioning during the last days of the quarter.
* S&P 500 futures rose 2.9 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 gained 11 points and Nasdaq 100 futures added 3.75 points.
* The Dutch biotechnology firm Crucell said Johnson & Johnson bought 14.6 million new Crucell shares for 302 million euros ($443.5 million) as part of a flu vaccine development deal.
* The Federal Reserve Bank of Chicago releases its National Activity Index for August at 8:30 a.m.(1230 GMT). The index read -0.74 the prior month.
* U.S. stocks fell for a third straight day on Friday on disappointing housing and durable goods data, while Research In Motion's Inc's lackluster results dented optimism about technology spending.