U.S. stock index futures were flat on Tuesday as investors awaited factory orders and pending home sales data for more signs about an economic recovery a day after the Dow and the S&P rallied to their highest closes in more than 15 months.

U.S. automakers are to release December auto sales, and economists surveyed by Reuters expect median annualized domestic sales of 3.90 million cars and 4.45 million trucks. In November, sales were 3.87 million cars and 4.44 million trucks.

The Commerce Department is to report November factory orders at 10 a.m. EST. Economists see a rise of 0.5 percent, compared with a 0.6 percent gain in the prior month.

Kraft Foods Inc sold its North American frozen pizza unit for $3.7 billion to Swiss food giant Nestle AG and sweetened its offer for Britain's Cadbury Plc.

Nestle said it does not intend to bid for the British confectioner, ending speculation of a potential rival offer.

S&P 500 futures rose 0.5 points 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 rose 1 point, and Nasdaq 100 futures fell 0.25 points.

The National Association of Realtors will release pending home sales for November at 10 a.m. EST. Economists look for a 2.0 percent decline, compared with a 3.7 percent rise in the previous month.

Google Inc is expected to unveil its highly anticipated smartphone in its first foray into an increasingly crowded market that could shape the future of the company's advertising business.

Apple Inc is set to release a new tablet device later this month, the Wall Street Journal reported Monday, as anticipation builds about its next big product launch since the iPhone.

(Reporting by Angela Moon; editing by Jeffrey Benkoe)