Golden Gate Bridge officials are getting closer to seismically strengthening the center portion of the span.

Seismic work on the northern approach, southern approach and the north anchorage house — the box-like structure that holds all the cables coming off the span that tie down the bridge — has been completed.

Work on the center suspension segment was saved for last because it is least susceptible to collapse in a major quake, bridge officials said. But it still could see major damage in a large temblor, and efforts to get the work off the ground are sharpening.

“It’s a large-scale job,” said Ewa Bauer, chief engineer of the bridge. “It involves a lot of work that has to be done not only with construction, but engineering knowledge.”

Bridge officials plan a trip to Washington, D.C., later this month to inquire about funding and gauge the interest of the new administration in the project.

The work won’t be cheap. The final phase of the seismic effort is pegged between $450 million and $500 million. But the bridge is considered a “lifeline” facility in the Bay Area, needed to reach people in potential emergencies and a key driver in the region’s economy.

“The bridge won’t collapse in a big earthquake, but there could be significant damage,” said Priya Clemens, bridge spokeswoman. “We are hoping to go out to advertise for the contract later this year. It’s a key project.”

It has been a long journey for the larger seismic project, which began in 1998. Initially the work was to have cost roughly $300 million but has since increased to more than $900 million as prices have gone up over time and bridge officials were forced to further gird the bridge after the 9/11 attacks.

The terror attack, which occurred in the early stages of the seismic retrofit project, forced bridge officials to rethink their plan beyond earthquakes. Officials examined ways to “harden” the towers “to protect against blast” in 2005.

Presently the bridge is safe, with span officials noting the north and south ends could sustain an 8.3-scale quake. The suspension section could withstand a large earthquake, bigger than a 7.0, but there would be extensive damage and the bridge would likely have to be closed for a long period.

The almost 80-year-old bridge was given a “good” rating by federal inspectors in terms of condition last year. Only an “excellent” is a better designation and typically given to new spans.