May 10 (Reuters) - The U.S. auto safety regulator said

on Friday it was opening a preliminary evaluation into 210,960

Ford vehicles following complaints alleging diesel fuel

leaks that may result in a fire.

The National Highway Traffic Safety Administration said its

Office of Defects Investigation has received 27 complaints,

including 12 reports of fires and a total of four injuries, and

that it would investigate Ford F-250, 350, 450, and 550 Super

Duty vehicles equipped with 6.7L diesel engines of model years

2015-2021.

The agency said a fracture in the secondary fuel filter in

the vehicles could result in a fire, as the proximity of the

filter to high heat sources creates a potential for

auto-ignition thermal events and fires.

The NHTSA has contacted the filter's maker, Allevard Sogefi

USA, and said it learned the secondary fuel filter is tested to

operate at reduced levels of pressure during the manufacturing

process, compared with the possible maximum operating pressure

in the fuel system of the vehicle.

Ford and Allevard Sogefi USA's parent Sogefi were

not immediately available for a comment.

The agency's preliminary evaluation is the first step to

determine whether the vehicles pose an unreasonable risk to

safety. It could close the investigation without taking any

potential action.

Separately, the NHTSA said on Thursday it had "significant

safety concerns" over Ford's recall of more than 42,000 SUVs

over concerns on fuel leaks that could lead to an engine fire.

While Ford had proposed an engine control software update

and installation of a drain, the NHTSA said the company's plan

"does not address the root cause of the issue and does not

proactively call for the replacement of defective fuel injectors

prior to their failure".