* Only a bit of promised $1.4 billion has been delivered

* Economy leaves U.S. security companies anxious for work

* Thirty to forty U.S. companies to benefit (Adds information about additional funding, quote; paragraphs 15, 20)

By Mica Rosenberg

MEXICO CITY, July 16 (Reuters) - As Mexico battles to keep a lid on raging drug war violence, U.S. companies are fighting over millions of dollars in contracts for military equipment and training under a long-promised U.S aid package.

Private U.S. security firms will get the bulk of a $1.4 billion package pledged by the United States in 2007 to help its southern neighbor crush rampant drug gang carnage. Only a fraction of the aid has been delivered so far.

Almost all of an initial $400 million tranche approved by the U.S. Congress in 2008 and being released bit by bit to buy helicopters and inspection gear and train Mexican police will be doled out to 30 or 40 U.S. companies, said a U.S. embassy official, who spoke on condition of anonymity.

The state-of-the art equipment, promised by former President George W. Bush at a meeting with President Felipe Calderon in the colonial city of Merida, is badly needed in Mexico as the death toll from a 2 1/2-year drug war tops 12,800.

"We would love to get in on some of that Merida money," said Scott Newman, an executive from Texas firm Texcalibur, which specializes in bulletproofing cars used in war zones.