UPDATE 1-Pickens miffed by NBC's rejection of "Iran" ad

(Adds details from letter to NBC Universal CEO)

NEW YORK, Aug 27 (Reuters) - NBC Universal has refused to broadcast an advertisement by U.S. oil tycoon T. Boone Pickens in which he questions America's dependence on foreign oil and calls for a switch to cars that run on natural gas.

Pickens said in a statement on Wednesday that the commercial has been cleared by every U.S. television network except for NBC Universal and called on the unit of General Electric Co (GE.N: Quote, Profile, Research, Stock Buzz) to reconsider its rejection.

In the 15-second ad entitled "Iran," Pickens says: "Get this one, Iran is changing its cars to run on natural gas and we're not doing a thing here."

"They're doing this to use less oil and sell it for a $120 a barrel. We can switch our cars to natural gas and stop sending our dollars to foreign countries," says Pickens, a billionaire oil investor who funded the "Swift Boat" attacks on Democratic presidential nominee John Kerry in 2004.

NBC Universal did not immediately return calls for comment.

Pickens, a frequent commentator on NBC Universal's cable business channel, CNBC, said in a letter to NBC Universal Chief Executive Jeff Zucker that the ad aimed to educate the public.

"We are puzzled by your decision not to run this ad because by not running it, you are selectively applying the First Amendment and denying your viewers access to information that is important to their education and understanding of the issue of energy independence," the letter said. (Reporting by Ritsuko Ando; Editing by Andre Grenon)