(Reuters) - Four major U.S. airports plan to speed up security checks by automating the distribution of bins for travelers' carry-on bags, the U.S. Transportation Security Administration (TSA) and American Airlines Group Inc said on Tuesday.

American's hubs in Los Angeles, Chicago, Dallas/Fort Worth and Miami will open the automated lanes this fall, which are expected to decrease wait times by 30 percent, the airline and TSA said in a joint statement.

Long security lines at U.S. airports this spring caused thousands of travelers to miss their flights and prompted criticism of TSA by airlines and other industry groups.

In an interview last month, American's CEO Doug Parker said the world's largest airline was working with airports to roll out the faster lanes, already in place at rival Delta Air Lines Inc's Atlanta hub.

At the four airports, automated conveyer belts will move bins for carry-on luggage through X-ray machines and divert those with suspicious items to a separate area, preventing bottlenecks. After screening is complete, the belts automatically move the bins back to the start of each lane.

American and TSA also said they plan to add computed tomography, or CT, scans for carry-on bags at a checkpoint in Phoenix by year-end.

The technology, currently in use for checked luggage, could allow travelers to leave carry-on liquids and laptops stowed in their bags.

"Think of the time - and bins! - that saves," American's Chief Operating Officer Robert Isom said in a letter to employees on Tuesday, shared with Reuters, noting that the airline is spending nearly $5 million on the new lanes.

"Neither initiative is a slam dunk to solve TSA woes, but they are both huge steps in the right direction," he said.

American has said the TSA must add enough staff to handle checkpoints during peak travel times, without relying on airlines to contract extra airport staff. Earlier this year, TSA projected it will screen 15 percent more people than in 2013, with 12 percent fewer agents.

TSA may deploy CT scans elsewhere if the Phoenix pilot program succeeds, according to the statement.

(Reporting by Jeffrey Dastin in New York, editing by G Crosse)