NHTSA Administrator Mark Rosekind told reporters that he expects agency staff to present a plan of options in each case early next month and vowed to be as aggressive as possible to minimize dangers posed by the deadly defects.

"We're going to look at every option, and we'll be as aggressive as possible," he told reporters on the sidelines of a NHTSA conference to examine ways to increase the effectiveness of automotive recalls.

Rosekind, a former member of the National Transportation Safety Board, spoke most forcefully about Fiat Chrysler .

Regulators have considered reopening an investigation into whether the automaker needs to take more action and has examined the most recent data on how fast it is adding hitches to the Jeeps to help protect the fuel tank from low-speed rear-end collisions.

"To be explicit, the situation has gotten worse ... the numbers came out, they're horribly low," he said. "Those translate into lives at risk, and more lives have been lost and people hurt. That's unacceptable."

Earlier this month, a jury awarded $150 million to a family that sued Fiat Chrysler for the 2012 death of their four-year-old son in a 1999 Jeep Grand Cherokee with a fuel tank mounted behind the back axle.

The 1999 Grand Cherokee was not included in a June 2013 recall of 1.56 million Jeep SUVs. It would have been had NHTSA not agreed with FCA to limit the recalls. The agency had earlier pushed for a wider recall of 2.7 million Jeeps.

Rosekind was also critical about Takata's actions on air bag inflators, which have been linked to at least six deaths and dozens of injuries, adding the Japanese manufacturer has provided significant help to investigators sifting through 2.5 million company documents.

Takata air bags have been found to explode, sending shards of metal into passenger compartments. An air bag recall has affected about 25 million vehicles from about a dozen automakers globally since 2008.

Rosekind has raised expectations for reform of an agency blamed for missteps on auto defects over the past decade. But he expressed concern about flagging enthusiasm in Congress to grant the funding and authority he says NHTSA needs to reduce the annual U.S. toll of highway deaths and injuries.

On Tuesday, a House appropriations panel proposed raising NHTSA funding by $6.5 million in fiscal 2016, compared with a $78 million increase sought by the Obama administration.

"It raises pretty significant concerns," Rosekind said of the legislation. "We're talking about a pretty big gap."

(Reporting by David Morgan; editing by G Crosse and Susan Heavey)

By David Morgan