"This is all just a proposal," Gibson says, explaining that another option under consideration would leave the existing building intact, and yet another would renovate it. The existing 561,559-sf tower at 11000 Wilshire Blvd., built in 1970, houses the FBI and a number of other federal agencies, with the FBI taking up about nine floors of the structure.

The new towers would house the field office headquarters of the FBI, which now has offices both in the federal building and in Downtown Los Angeles. Under the second alternative, the existing tower would remain intact and two new towers would be built. The third alternative would be "no action whatsoever," Gibson says.

The new headquarters would not replace any of the existing FBI field offices, which the bureau maintains at a number of locations throughout Southern California. However, it would consolidate operations now housed at the Federal Building and the Downtown L.A. offices.

The final environmental impact report for the proposal is due to be released at the end of April, followed by a 30-day public comment period. Gibson says that at the earliest, the beginning of construction would be years out, with the final construction on the two-phase project due to be finished in 2017.

The Federal Building is part of a complex of US government agencies and facilities in Westwood, including a Veterans Administration medical center, a former VA medical center and a VA cemetery. The Westwood site is one of 35 locations that the FBI examined in its search for a suitable regional facility.