U.S. stocks were set to open little changed on Tuesday as geopolitical concerns in Japan and Libya kept investors nervous.

A U.S. Air Force F-15E fighter jet crashed overnight in Libya, apparently due to a mechanical failure and its crew were safe. U.S. military said.

Smoke and steam rose from two of the most threatening reactors at Japan's quake-crippled nuclear plant, suggesting the battle to avert a disastrous meltdown and stop the spread of radiation was far from won.

S&P 500 futures rose 0.9 point and were in line with 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 were up 17 points, and Nasdaq 100 futures added 4.75 points.

European Central Bank President Jean-Claude Trichet and other ECB policymakers have reiterated they are ready to act quickly to guard against inflation.

Sanofi-Aventis and Merck & Co abandoned plans for a joint animal health powerhouse with $5 billion in sales, citing the increasing complexity of disposals and regulatory reviews needed for the deal.

Design software maker Adobe Systems is expected to deliver its fourth consecutive quarterly improvement in profit, driven by strong adoption of its software. Wall Street has priced in a profit of 57 cents per share, up from 40 cents per share one year ago.

European shares pared gains in morning trade on Tuesday as the latest developments in Libya promoted fresh jitters.

On Monday, the Dow Jones industrial average <.DJI> gained 178.01 points, or 1.50 percent, to 12,036.53. The Standard & Poor's 500 Index <.SPX> climbed 19.18 points, or 1.50 percent, to 1,298.38. The Nasdaq Composite Index <.IXIC> added 48.42 points, or 1.83 percent, to 2,692.09.

(Reporting by Angela Moon; Editing by Kenneth Barry)