US STOCKS-S&P, Dow futures up ahead of Citi; Apple falls

* Apple off as CEO takes medical leave; to post results

* Citigroup seen reporting 4th quarterly profit in row

* Futures: S&P up 0.8 pt, Dow up 25 pts, Nasdaq off 14.5

* For up-to-the-minute market news see [STXNEWS/US] (Updates with analyst quote)

By Angela Moon

NEW YORK, Jan 18 (Reuters) - S&P and Dow index futures rose on Tuesday as investors were upbeat about corporate earnings, but Apple weighed on Nasdaq futures after its chief executive took another medical leave.

Apple Inc <AAPL.O> shares fell nearly 5 percent to $331.37 in premarket trade after it said CEO Steve Jobs was taking his third medical leave since 2004, reviving concerns about the future of the maker of the iPad and iPhone. Apple is due to report results later Tuesday. For details, see [ID:nSGE70G0AY] and [ID:nL3E7CI0LO]

Citigroup Inc <C.N>, which took $45 billion in bailout funds during the financial crisis, is widely expected to report its fourth consecutive quarterly profit before the opening bell, signaling its recovery is largely completed. Analysts looked for a quarterly profit of 8 cents per share, according to Thomson Reuters I/B/E/S. [ID:nL3E7CG019]

The stock was up 1.1 percent at $5.18 in premarket trade.

Investors also braced for results from International Business Machines Corp <IBM.N>. [ID:nN14244724]

"Apple is weighing on the technology sector but it's all about earnings today, and investors are hopeful after what we've gotten so far in this earnings season. The quality of earnings that are coming in has improved a lot," said Peter Cardillo, chief market economist at Avalon Partners in New York.

S&P 500 futures <SPc1> rose 0.8 point and were slightly 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 <DJc1> gained 25 points, while Nasdaq 100 futures <NDc1> lost 14.5 points.

In corporate news, Goldman Sachs Group Inc <GS.N> will limit its private placement of shares of Facebook, the social networking site, to investors outside the United States, citing "intense media coverage."

South African retailer Massmart's <MSMJ.J> shareholders have accepted a takeover bid from U.S. group Wal-Mart Stores Inc. <WMT.N> [ID:nLDE70G0MZ]

European stocks hit a 28-month high Tuesday, led by mining shares after Rio Tinto Plc's <RIO.L> output figures pleased investors and as metal prices climbed.

The S&P 500 ended a seventh straight week of gains with a banks-led rally amid healthy volume after encouraging financial results from JPMorgan. (Reporting by Angela Moon; editing by Jeffrey Benkoe)