In a rare move, Chrysler today rejected a request by U.S. auto safety officials to recall 2.7 million Jeep Grand Cherokees and Liberty SUVs to fix fuel tanks that federal officials linked to 51 deaths, but which Chrysler called "safe and ... not defective."

The face-off sets up a little-used process by which the National Highway Transportation Safety Administration could take Chrysler to court and order it to fix the SUVs. The agency acted after four years of pushing by auto safety advocates, who first complained that Chrysler put lives at risk when it sold the 1993-2004 Grand Cherokee and 2002-2007 Liberty SUVs with plastic gas tanks built behind the rear axle, leaving them exposed to damage in a crash.

Automakers almost always launch recalls of their own initiative or after a NHTSA investigation shows the agency believes a safety defect exists to avoid a legal and public relations hit. The few times an automaker has resisted a recall request over the past two decades — as Ford did in 2011 when the agency found air bags in 1.5 million F-150 trucks were defective — the automaker has eventually given into NHTSA.

But Chrysler said NHTSA's conclusions were incorrect, that the agency's reading of the data was flawed and that the Jeeps met all applicable safety standards.

"The company does not agree with NHTSA’s conclusions and does not intend to recall the vehicles cited in the investigation," the company said in a statement.

The debate dates to 2009, when the Center for Auto Safety first asked NHTSA to probe fires in Jeep Grand Cherokees, noting that the SUV had been built with a gas tank between the bumper and rear axle. Since the infamous Ford Pinto, most automakers had redesigned their vehicles to move the fuel tanks ahead of the rear axle to better protect it from crashes. Because the Grand Cherokee's bumper rode higher than most cars, CAS also contended the fuel tank was even more exposed.

In 2005, Jeep redesigned the Grand Cherokee and moved the fuel tank in front of the axle. Since then, the Center for Auto Safety says, no one has died from a post-crash fire in a Jeep Grand Cherokee.

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NHTSA didn't officially open a probe of the vehicles until 2010, and gathered accident data and test results from Chrysler along with several other automakers. In its letter to Chrysler, NHTSA said it had found 44 deaths in 32 rear-end crashes with fires related to the Grand Cherokee's fuel tank, and 7 deaths from 5 crashes in Jeep Liberty SUVs — both of which were far more common than other models of SUVs. It also found 27 rear-end crashes where a Liberty or Jeep Grand Cherokee caught fire, but no one was injured.

Chrysler responded that the HDPE fuel tanks met NHTSA's own safety standards for rear crash impact, but NHTSA contended that the standard is a minimum target, and "does not require NHTSA to ignore deadly problems."

The automaker says its reports show that the problems "occur less than once for every million years of vehicle operation," which it calls similar to other models from the same period.

The Center for Auto Safety has a far higher count of fires from all types of crashes — 201 in the affected Grand Cherokees alone, with 285 deaths. Two months ago, CAS Executive Director Clarence Ditlow wrote to Chrysler Chairman Sergio Marchionne asking him to recall the SUVs, citing the recent fire deaths of two four-year-old children in separate crashes.

"When will the killing end, when will 4-year olds stop being burned to death in Jeep Grand Cherokees?" Ditlow said.

If Chrysler does not budge, NHTSA can hold a public hearing, then officially declare the Grand Cherokee and Liberty defective. While Chrysler can then challenge the decision in court, it also opens itself to liability claims and bad press. NHTSA suggests a potential fix in its letter — adding a skid plate sold as an option on some Grand Cherokees that would protect the tank in crashes — but it may take a judge to rule whether Chrysler has to do things NHTSA's way.