NEW ORLEANS  The United States is back in the leadership spot in the highly competitive wireless market, thanks in large part to the billions of dollars that the industry has poured into expanding wireless networks across the country, according to the heads of the top four largest carriers.

However, that standing is not guaranteed, and during a panel at the CTIA Wireless 2012 show here, the executives said they see a host of challenges ahead, from finding more spectrum to handle the rapidly growing amount of data that is crossing the networks to an apparent gulf in trust between the carriers and their customers.

The executives statements echoed comments made earlier in the day by Julius Genachowski, chairman of the Federal Communications Commission (FCC), who said that mobile broadband will be a key economic driver worldwide.

The U.S. is leading this revolution, Genachowski said. We have now regained our leadership in mobile.

Dan Mead, president and CEO of Verizon Wireless, agreed, noting that his company and others have spent billions of dollars upgrading their networks and lead the world in the race toward 4G networks. Mead called the wireless industry one of the countrys greatest economic growth engines.

However, he echoed a familiar warning about the looming spectrum crunch that is threatening the growth. The adoption of mobile devicesin particular, smartphones and tabletsis driving the skyrocketing growth of traffic that is running across the wireless networks. The FCC has said that network traffic by 2015 will be 25 to 50 times that of 2010, and Mead said that without more spectrum, demand will exceed capacity by 2014.