Federal safety regulators received more than 260 complaints over the past 11 years about General Motors vehicles that suddenly turned off while being driven, but they declined to investigate the problem, which GM now says is linked to 13 deaths and requires the recall of more than 1.6 million cars worldwide.

A New York Times analysis of consumer complaints submitted to the National Highway Traffic Safety Administration found that since February 2003 it received an average of two complaints a month about potentially dangerous shutdowns, but it repeatedly responded that there was not enough evidence of a problem to warrant a safety investigation. The complaints — the most recent of which was filed Thursday — involved six GM models that the automaker is now recalling because of defective ignition switches that can shut off engines and power systems and disable air bags. GM said the first recall notices were mailed Friday to the owners of the vehicles.

Many of the complaints detailed frightening scenes in which moving cars suddenly stalled at high speeds, on highways, in the middle of city traffic, and while crossing railroad tracks. A number of the complaints warned of catastrophic consequences if something was not done.

"When the vehicle shuts down, it gives no warning, it just does it," wrote one driver of a 2005 Chevrolet Cobalt. "I drive my car to and from work praying that it won’t shut down on me while on the freeway."

Another driver wrote of the same model: "Engine stops while driving — cannot steer nor brake so controlling the car to a safe stop is very dangerous."

To the mounting complaints, the safety agency sometimes responded with polite but formulaic letters similar to one it sent in December 2010 to Barney Frank, then a congressman from Massachusetts, who had written on behalf of a distraught constituent whose 2006 Cobalt kept stalling. In the letter to Frank, the agency said it had reviewed its database of complaints to determine if a "safety defect trend" existed. "At this time, there is insufficient evidence to warrant opening a safety defect investigation," the letter concluded.

Failure to recognize a pattern in individual complaints has been a problem for the safety agency before. In the late 1990s, it was criticized for failing to detect a wave of highway rollovers in Ford Explorers with Firestone tires, a problem that was eventually linked to 271 deaths.

In response, Congress passed a law in 2000 requiring automakers to report to the safety agency any claims they received blaming defects for serious injuries or deaths, so the government would not have to rely only on consumer reports. Since 2003, GM has reported at least 78 deaths and 1,581 injuries involving the now-recalled cars, according to a review of agency records. Though the records mention potentially defective components, how many of these records were related to the ignition problem is unclear. Even with that additional information, regulators appear to have overlooked disturbing complaints of engine shutdowns.

"We need to make it clear to both industry members and regulators that adverse events must be immediately reported and analyzed to ensure public safety," said Rep. Diana DeGette of Colorado, a Democrat on the House Energy and Commerce Committee. The panel’s staff is scheduled to meet with the safety agency Monday.

The safety agency has repeatedly suggested that it failed to act over the years because of a lack of a critical mass of evidence that suggested a problem beyond isolated incidents.

In a statement emailed to The New York Times, a spokesman noted that over the past seven years, the agency’s investigations in other cases have resulted in 929 recalls of more than 55 million vehicles. The agency "uses a number of tools and techniques to gather and analyze data and look for trends that warrant a vehicle safety investigation and possibly a recall," the statement said. The agency said 260 complaints amounts to about .018 percent of the vehicles under recall.

In a telephone interview, Frank Borris, the director of the agency’s office of defects investigation, said that two years ago, the agency began using IBM software to help look for patterns. Judgments are made by "really well-seasoned automotive engineers who leverage a lot of technology and lean on past precedent about when to open, when to close, and when to push for a recall," Borris said. "It’s no magic formula."

The agency’s chief counsel, Kevin Vincent, said that to warrant an investigation, the case must pass a legal test of "unreasonable risk to safety."

"That term ‘reasonable’ is a legal term, which is very elastic and means a lot of different things in a lot of different contexts," he said. "Each case is a different fact pattern."

The recall has thrown GM into turmoil just as it was emerging from the shadow of bankruptcy under the leadership of a new chief executive, Mary T. Barra, and as the safety agency stepped up pressure on the company in late February by launching an investigation into the "timeliness" of GM’s "defect determination." Last week the agency sent the company 107 questions, demanding it explain why it had waited so long to recall the vehicles.

But The New York Times review of thousands of complaints stored in the agency’s public database raises questions about the agency’s own timeliness. The newspaper analyzed nearly 8,000 complaints about the recalled models to find instances when drivers may have been affected by faulty ignition. The 260-plus total includes only complaints that mentioned a moving car stalling unexpectedly. It does not include the complaints filed about basic ignition problems on these models, like trouble starting or stopping a car’s engine, or failures of the power steering mechanism, even though these could have stemmed from an inadvertent ignition shutdown. People may have filed multiple complaints about the same car.

Greg Martin, a GM spokesman, said the company monitors complaints to the NHTSA about its vehicles but declined to say how the agency responded to ignition switch complaints.

By the time the agency wrote to Frank in 2010, it had received more than 170 complaints about unexpected stopping or stalling of the recalled GM models, and 35 specifically for the 2006 Cobalt. The Cobalt has been a particularly problematic model for GM. In 2010, the automaker recalled some of the vehicles for power steering failure, and in December 2005, it told dealers that owners should remove unessential items from key chains.

The expectation of the 2000 law, known as the Tread Act, was that the measure would help government regulators flag trends months or years earlier than they would if they relied on consumer complaints alone. The law was used to punish Toyota for failing to report unintended accelerations; that company paid a civil penalty of $16.4 million under the act. But it does not appear to have helped the government identify problems faster.

Joan Claybrook, who led the safety agency during the Carter administration, said, "The ability to spot trends is a huge issue, and NHTSA has not got it under control by any means."

The safety agency did hire contractors to look into two fatal crashes that killed three teenagers and have since been linked to the ignition problems, after local accident investigators recommended inquiries. Both involved 2005 Chevrolet Cobalts, and in both cases, the contractors found that air bags had not deployed and the cars’ power had shifted into "accessory" mode — essentially the state a parked car is in when occupants want to listen to the radio. In an April 2007 report of the second crash, the contractors cited six complaints in the agency’s database that appeared to match that situation.

Many consumers who approached the agency were met with institutional silence.

"This is a safety issue if there ever was one," wrote Laura Denti of Toms River, N.J., in a letter both to GM customer service and to the safety agency on June 29, 2005, citing three times when her daughter’s new 2005 Cobalt shut down abruptly while in operation. The letter also referred to a previous letter she had sent.

"I don’t recall them ever responding," Denti said in an interview last week.

Denti’s daughter Samantha, now 28, described in a separate interview her excitement when her mother leased the car for her.

"It was a beautiful car. It was red. It was great," she said.

But a few months after she got it, she said, the car suddenly died at a busy intersection.

"People were swerving and honking. They didn’t expect the car to be there," she said.

Shortly after, on a trip to Tennessee, the car stalled on a highway exit ramp.

Both times, mother and daughter conveyed their alarm to the dealer, demanding an explanation and remedy. Both times, the dealer recommended removing extra keys from the key chain, saying they could jostle the ignition switch into shutting off. After a third stall-out, the Dentis terminated the lease.

"I ended up owing thousands of dollars extra," Samantha Denti said. "My mom said, ‘We’ll pay. This car is a death trap. We want out of it.’"

The recall covers six models from years between 2003 and 2007: 2005 -07 Chevrolet Cobalts; the 2007 Pontiac G5; 2003-07 Saturn Ions; 2006-07 Chevrolet HHRs; 2006-07 Pontiac Solstices and the 2007 Saturn Sky. Both the agency and the company are warning motorists that if they must drive a recalled vehicle, no keys other than the car key should be on the key chain to eliminate potential jostling that could shut down the ignition.

In announcing the recalls, GM said the ignition defect may have been responsible for 31 accidents and 13 deaths, but it has declined to disclose the names of those who died or the dates, location or other details of the crashes. The company said it had been "involved in claims and lawsuits" related to the ignition problem, but did not disclose how many settlements had been reached.

"Is my daughter’s name in the 13?" asked Mary Ruddy of Scranton, Pa., in an interview.

The safety agency’s database contains at least four complaints from Ruddy, whose 21-year-old daughter Kelly was killed Jan. 10, 2010, while driving a 2005 Chevrolet Cobalt. Ruddy’s complaints were not counted in the review because they did not specify stalling on the road.

In her filings to the agency, the most recent on Feb. 18, Ruddy said her daughter’s car overturned and rolled, ejecting her onto the highway.

"I knew the minute I got the news that my daughter was killed so violently and that it did not involve another car that it had to be a mechanical failure," she wrote.

In April 2010, she received a recall notice citing failures in the power steering systems of the ’05 Cobalt, and she contacted GM, which, she said, sent three representatives — an automotive engineer, a man who identified himself as an "accident reconstructionist" and a photographer — to examine the wrecked vehicle and remove its "black box" for data.

Ruddy said that despite repeated requests, the company had declined to return the black box or share the data, and sent only an "air bag deployment report" that she said was incomprehensible to her and her lawyer.

GM said its policy is to return any part, like a black box, to the owner of the vehicle if requested.

She said she had received form letters from the agency saying only that it had received her complaint. "They never called me and never spoke to me."

"I just want someone to hear me," she said. "We’ve had no closure. We still have no answers."

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