* Senators push Takata to expand recall across U.S.
* Two Senators raise possibility of 6th air bag-linked death
* Takata stops short of taking "full responsibility" for deaths (Adds comments by NHTSA official, lawmakers, other details from hearing)
By Eric Beech and Ben Klayman
WASHINGTON/DETROIT, Nov 20 (Reuters) - An executive from Japan's Takata Corp apologized at a Senate hearing on Thursday to the victims of defective air bags that can rupture upon deployment and shoot metal shards into cars, but stopped short of taking full responsibility for deaths linked to the scandal.
Separately, an executive from Honda Motor Co, whose vehicles have been most impacted, acknowledged during testimony that the automaker could have acted faster to recall and replace the air bags.
The hearing by the Senate Commerce Committee also focused on whether regulators and the auto industry have yet captured the full scope or the exact cause of the defect that has affected millions of vehicles and been linked to at least five deaths.
"We now have a new problem that we are addressing, which is in effect a live hand grenade in front of a driver and a passenger," said Democratic Senator Bill Nelson, who chaired the hearing, the first to examine the deadly air bag saga that came to light in 2008 and has escalated in recent months.
So far around 16 million cars with Takata air bags have been recalled worldwide, with more than 10 million of those in the United States.
The hearing held high stakes for Takata, which is facing a criminal probe into the scandal, more than 20 class actions and a probe by the U.S. National Highway Traffic Safety Administration.
When pressed by Republican Senator Dean Heller to take "full responsibility" for five deaths linked to the air bags, Hiroshi Shimizu, senior vice president for global quality assurance at Takata, consulted a colleague multiple times.
He answered that two of the five fatalities were still under investigation, but acknowledged "anomalies" with Takata air bag parts involved in some fatal accidents. Shimizu said in his prepared comments that Takata was "deeply sorry and anguished about each of the reported instances."
Rick Schostek, Honda's North American executive vice president, was also pressed about the slow rollout of recalls that started in 2008. It was only this month that the automaker turned its "safety improvement campaign" into a formal recall.
"I think we acted with urgency, but do I think we could have moved faster in some respects? I absolutely do," Schostek said.
Automakers, regulators and Takata - which supplies one in five air bags globally - have yet to pinpoint why these air bags are at risk.
Shimizu said the company believes that the "root causes" of the air bag inflator ruptures are a combination of three factors: the age of the inflator, persistent exposure to high humidity, and problems in production.
The recalls so far have been focused on humid areas. That approach was questioned at a news conference before the hearing, when two U.S. senators linked the air bag defect to a 2003 death in Arizona, which is not considered a humid area.
Charlene Weaver, 24, died in a Takata air bag-related accident while she was a passenger in a 2004 Subaru Impeza in Arizona, her sister, Kim Kopf, said. That car was not recalled until July of this year.
The senators raised the possibility of Weaver's death as the sixth fatality linked to Takata air bags and the first reported outside of Honda vehicles.
A Subaru spokesman said the company was not aware of one of its models being involved in a fatal accident in Arizona.
Democratic Senator Ed Markey said the incident shows the need for a nationwide recall. "Every single one of these Takata air bags could be a ticking time bomb," he said.
Shimizu said Takata plans to ramp up production of replacement air bag parts to 450,000 units per month, but that might not be fast enough to meet the demand of recalls.
NHTSA on Tuesday called on Takata and five automakers to expand their regional recalls of driver-side air bags to cover the entire United States, as senators have urged. But an official acknowledged on Thursday that such a move carries risks.
"At this point, a national recall of all Takata air bags would divert replacement air bags from areas where they are clearly needed, putting lives at risk," said NHTSA Deputy Administrator David Friedman.
Some automakers, such as Chrysler, have notified owners they should have their air bags studied rather than replaced.
Democratic Senator Claire McCaskill, a former prosecutor, criticized executives from Honda and Chrysler for not being more aggressive in recalling vehicles.
"We have got to get out of this defensive crouch about liability litigation and get into an offensive position about making sure drivers are safe," McCaskill said. (Additional reporting by Bernie Woodall in Detroit, Doina Chiacu and Elvina Nawaguna in Washington; Writing by Julia Edwards; editing by Karey Van Hall and Matthew Lewis)