The Federal Aviation Administration – Renton’s fourth-largest employer – is looking at new sites in five cities for an expanded regional headquarters.

Renton has been home to the FAA’s Northwest Mountain Region for 20 years. It has about 1,600 workers spread out over three buildings in the 1600 block of Lind Avenue Southwest.

Under a longstanding plan, the FAA is moving about 400 employees to the regional headquarters from California and Alaska, making the total workforce about 2,000.

Any city would covet that many well-paying federal jobs and the secondary benefits to the local economy.

Retaining the FAA headquarters in Renton “is the highest economic development project that we have going right now,” said Alex Pietsch, the administrator of the city’s Department of Community and Economic Development.

A loss of those jobs in Renton “is obviously very significant,” he said.

The federal General Services Administration, which is handling the search for the FAA, is looking for sites in Renton, Kent, Seatac, Tukwila and Des Moines for a new headquarters.

The FAA will need about 518,000 square feet to accommodate the demand for more space.

Pietsch said there are 10 possible locations for a new FAA headquarters in Renton, including the current one, spread out across the city.

“We think they would all be excellent homes for the FAA in the future,” Pietsch said.

He said he knows of no other competing city with 10 properties, many of which have offers from multiple developers willing to build on them.

“I am hopeful that Renton has a very good chance,” he said.

The City of Renton is willing to streamline its permit process for a new development and help with infrastructure improvements, Pietsch said.

Pietsch doesn’t believe there is any one building large enough in South King County to accommodate the FAA’s space needs. There is room to expand the FAA’s current footprint on Lind Avenue.

Ross Buffington, a GSA spokesman, said a decision hasn’t been made to build a new building, because it’s still possible an existing building could meet FAA needs.

The City of Kent is pressing hard to get the FAA to locate in Kent.

Kent, working with a developer and a construction firm, is offering a 15.5-acre site just off Highway 167 near Willis Street. The site is currently under consideration for a swimming pool.

The FAA is confining its search to near Renton because of labor agreements with its headquarters’ employees that any move to a new building wouldn’t disrupt their commute patterns, Buffington said.

The GSA and FAA want to sign a lease by spring 2011, with occupancy in September 2014, Buffington said.

About 200 people attended a meeting in late January on the lease offer, possibly the largest lease option currently in play in the Seattle area, he said.