The decision came so close to the opening date that officials decided not to proceed with an extravagant celebration planned to mark the completion of the bridge, which at $6.4 billion is the most expensive single piece of infrastructure in California’s history.

“There will be no public celebration,” Mr. Gordon said. “There will be a low-key chain cutting.”

The new stretch of the bridge is equipped with the latest in antiseismic design. But in March, 32 in a batch of 96 high-strength steel bolts holding shock-absorbing devices called shear keys snapped, a failure that Steve Heminger, the chairman of the committee, later described as “catastrophic.”

The defective bolts are being replaced with steel cable saddles. Last month, transportation officials said they would postpone the opening of the bridge until all the saddles were installed, pushing the opening date into December at the earliest. But some experts, including the bridge project’s chief engineer, favored the Labor Day opening because they argued that the new bridge, though incomplete, was already safer than the existing one.

In 1989, an earthquake caused a section of the eastern stretch’s upper deck to collapse, killing a driver and closing the bridge for a month. Another, potentially more devastating, quake could hit this area by 2033, according to government seismologists.