(Adds quote from report, paragraph 3)
By David Alexander
WASHINGTON, March 18 (Reuters) - Defense Secretary Chuck Hagel ordered steps to improve Pentagon security on Tuesday after reviews found the Navy Yard shooting that killed 12 people last year could have been averted if concerns about the gunman's mental health been properly handled.
Navy Yard shooter Aaron Alexis, a 34-year-old former sailor with a prior record of firearms complaints, had reported hearing voices and suffering from insomnia in the weeks leading up to Sept. 16, when he entered the Washington base and opened fire with a sawed-off shotgun.
Defense Secretary Chuck Hagel and Navy Secretary Ray Mabus released the results of three reviews of the shooting incident on Tuesday, including one that said the tragedy might have been averted had authorities not "missed opportunities for intervention."
"The reviews identified troubling gaps in DoD's (Defense Department's) ability to detect, prevent and respond to instances where someone working for us, a government employee, member of our military, or a contractor, decides to inflict harm on this institution and its people," Hagel told reporters.
Lawmakers in the Senate and House of Representatives welcomed the findings of the three reviews - one Pentagon, one Navy and one independent - and pressed the Defense Department to move forward with steps to improve the issuance and regular review of security clearances.
"There is a gaping hole in the current security clearance process that has enabled people who exhibit obvious signs of high-risk behavior to remain undetected," said Senator Susan Collins.
The Navy review found that Alexis' employer, an information technology company called The Experts that worked on defense contracts, had concerns about his mental state but did not report them. It said the Navy itself had earlier failed to properly evaluate and report his behavior while he was a sailor.
"The company leadership decided not to inform the government of adverse information concerning Alexis' emotional, mental, or personality condition, even when they had concerns that Alexis may cause harm to others," the Navy report said.
"This information was not reported to the government as required," it said. "Had this information been reported, properly adjudicated and acted upon, Alexis' authorization to access secure facilities and information would have been revoked."
The independent review ordered by Hagel concluded the Pentagon grants far too many people secret security clearances, as it did to Alexis, even though he never needed it to perform his Navy job.
The clearance in turn helped him obtain employment after leaving the Navy, with a defense subcontractor working on secret-level information systems at the Washington Navy Yard and other installations.
Alexis entered the Navy Yard the morning of Sept. 16 using his Defense Department access card and carrying a concealed sawed-off shotgun, the Navy report found. He killed 12 people and wounded four before being slain by police an hour and 10 minutes after first opening fire.
Hagel said he had accepted four key recommendations aimed at improving security, including moving to a system of continuous evaluation of people who have secret security clearances, rather than the current practice of not re-examining them for a decade unless derogatory information is presented to authorities.
He also agreed to the establishment of an insider threat management and analysis center within the Pentagon to take responsibility for the process under a top official, and to create an identity management software system that allows different services to share personnel information.
Hagel said three other proposals were being considered: reducing the number of people holding classified security clearances by 10 percent, conducting background checks in the Pentagon rather than externally, and working to improve mental health care in the department. (Editing by Bill Trott and Richard Chang)