Randall Walker, director of the Clark County Department of Aviation, said McCarran International Airport is adding traffic even faster than FAA projections.

But he said the report is useful for highlighting on a national level the importance of building capacity in places such as Las Vegas, where McCarran hosted 46.2 million passengers last year.

"Obviously, if the national airspace system is not functioning, that is going to affect our airport as well," Walker said.

A third terminal is already in the works for McCarran and it is expected to open in 2011. It will include 14 gates and is estimated to cost $1.8 billion. By 2017, Clark County Aviation officials hope to be operating a new airport near Primm that could support an additional 16 million passengers annually.

Against the backdrop of the world's busiest airfield, U.S. Secretary of Transportation Mary Peters on Tuesday praised Atlanta and Hartsfield-Jackson Atlanta International Airport for building another runway and new air traffic control towers. Peters also announced a $1 million grant to study further capacity expansion in Atlanta.

"By 2025, cities like Atlanta, Las Vegas, Chicago and San Diego are going to risk the lost revenue, lost business and lost appeal that comes with chronic delay," Peters said. "Atlanta's leaders will have to embrace new airports and new ways of thinking."

Federal Aviation Administration Administrator Marion Blakey said that the current number of air passengers is "sounding a siren that must be responded to" with a regional approach.

Airports in Boston, Cleveland, Los Angeles, St. Louis and Minneapolis-St. Paul have also recently opened new runways.

The FAA study began in 2003, reviewing 291 commercial service airports, and whittled that down to the 56 most at risk of overcapacity.

After the completion of the first version of this study in 2004, it was recommended that Atlanta expand immediately. The city made substantial improvements since, but aviation officials warned it will need to address growing passenger demand before 2025.

Four airports were identified as needing to expand capacity immediately -- New York's LaGuardia Airport, Newark (N.J.) Liberty International, O'Hare International Airport in Chicago and Fort Lauderdale-Hollywood (Fla.) International.

The Associated Press contributed to this report.