* S&P futures trade in tight range below 1,333
* Southwest falls after planes grounded for inspection
* Futures: Dow up 15 pts; S&P up 2.5 pts; Nasdaq up 9 pts (Updates with grounding of Southwest planes, Pfizer selling unit, updates prices, comment, byline)
By Rodrigo Campos
NEW YORK, April 4 (Reuters) - U.S. stock index futures edged higher on Monday, with the S&P 500 facing a level where selling has clustered in recent sessions.
S&P 500 futures traded in a tight range below 1,333. The benchmark has been unable to close above that level since mid-February, although it was briefly pierced on Friday.
That level is double the 12-year low hit in March 2009 and is not far from 1,344, the S&P's 2011 high and its highest since June 2008.
On Friday, the S&P closed its best two-week period since December and the Dow industrials <.DJI> hit its highest intraday level since June 2008.
"The speed with which we moved up is putting a bit of a curb on a further rally," said Rick Meckler, president of investment firm LibertyView Capital Management in New York.
"Certainly there are plenty of traders who will be using this runup to try and take profits and get back at a better point. It's hard to maintain the speed of this advance," he said.
The lack of significant economic data on Monday, nuclear and other quake-related problems in Japan and unrest in Libya, Syria and other states in the oil-rich region could translate into low volumes in Wall Street. Last week was the lowest in volume so far in 2011.
S&P 500 futures
Southwest Airlines Co
In the latest M&A activity, Pfizer Inc
Some nervousness over the political unrest in the Middle
East and North Africa continued to linger in financial markets,
with Brent crude
In other company news, Nasdaq OMX Group Inc
Separately, Deutsche Boerse
The U.S. Bureau of Ocean Energy Management said on Sunday
it had not struck a deal with BP