WASHINGTON (AFP) - General Motors (GM) chief Mary Barra apologised on Tuesday for the United States (US) automaker's failure to fix defective ignition switches linked to 13 deaths and vowed the company would "do the right thing". The manufacturer is under fire for not recalling Chevrolet Cobalts, Saturn Ions and other GM models over the past decade, despite its own technical evidence that the cars were potentially deadly. GM eventually issued mass recalls this year.

Ms Barra said GM has acknowledged the problem, launched an exhaustive review to determine what and who is responsible, and pledged top-to-bottom changes in shifting from a "cost culture" to a focus on safety and quality.

"Today's GM will do the right thing," she told an investigations panel of the House Energy and Commerce Committee in Washington.

"That begins with my sincere apologies to everyone who has been affected by this recall," she added. "I am deeply sorry."

Lawmakers pointed to internal documents showing GM at first refused to change the faulty switches because doing so would have been too costly and expressed astonishment that the company went ahead with using the parts even though they did not meet GM standards.

"That is not something that I find acceptable," Ms Barra said.

Heaping pressure on the automaker, weeping relatives marched up Capitol Hill, clutching images of their loved ones, to demand accountability from GM and to tell how their children died in vehicles they said GM knew were faulty.

"Our daughters, sons, sisters, brothers, mothers, fathers, wives and husbands are gone because they were a cost of doing business, GM-style," said Ms Laura Christian.

Ms Christian's daughter Amber Marie Rose, 16, was killed in 2005 when a Cobalt's airbags did not deploy in a crash - possibly due to a faulty ignition.

'US$2 TOO MUCH'

The hearing is the first in what is likely to be a mounting pile of legal troubles for the US auto giant, including a US Justice Department probe and lawsuits from people injured and families of those who died in crashes allegedly tied to the ignition issue.

Analysts have already speculated that the trouble could cost the company billions of dollars in penalties and damages, on top of huge costs of the recalls themselves.

Lawmakers argued the tragedies could have been avoided if GM acted swiftly to fix a serious but inexpensive problem.

"Two dollars. That's how little this ignition switch could have cost to repair," said Senator Ed Markey. "But that was apparently US$2 too much for General Motors."

Also testifying was the acting administrator of the National Highway Traffic Safety Administration (NHTSA), the US auto safety agency under attack for not acting on its own evidence that the ignitions posed dangerous risks to drivers.

Several lawmakers said GM and NHTSA repeatedly missed or ignored red flags about the problems.

"It is important that we get to the bottom of this," said congresswoman Marsha Blackburn. "We want to know who knew what when - and Ms Barra that includes you."

GM PLEDGES TRANSPARENCY

Ms Barra, a lifetime GM employee, said: "More than a decade ago, GM embarked on a small car programme. Sitting here today, I cannot tell you why it took years for a safety defect to be announced in that programme.

"When we have answers, we will be fully transparent with you, with our regulators and with our customers."

GM has hired lawyer Kenneth Feinberg, who handled the September 11 and BP oil spill compensation cases, to study how it should address victims of the accidents.

"We do understand that we have civic responsibilities as well as legal responsibilities," Ms Barra said.

Legally, GM's 2008-2009 rescue by the government and bankruptcy reorganisation could protect it from liabilities before that, a scenario that has infuriated some lawmakers.

Since February, GM has recalled 2.4 million cars covering model years 2005-2010 over the faulty ignitions, which can abruptly switch into "accessory" or "off" position while in drive, especially when the car is jolted.

That can turn off the car's electrical systems, including safety airbags, preventing them from inflating in a collision.

GM's documentation shows it was first aware of a problem in 2001 when the cars involved were in pre-production.