(Reuters) - The U.S. Justice Department unveiled a broad probe on Tuesday into complaints that authorities were failing to aggressively investigate sexual assault reports in Missoula, Montana, citing more than 80 reported rapes there during the past three years.

The investigation includes a review of the handling of sexual assault and harassment reports at the University of Montana at Missoula, where at least 11 student-related sex assault cases have surfaced in recent months.

At least two members of the university's Big Sky Conference champion football team, the Grizzlies, have been accused of rape, leading to the recent dismissal of the football coach and the school's athletic director.

A central thrust of the federal investigation will focus on complaints that local law enforcement has failed to properly investigate and prosecute sexual assaults on women in Missoula due to gender discrimination, the Justice Department said.

"The allegations that the University of Montana, the local police department and the county attorney's office failed to adequately address sexual assaults are very disturbing," Attorney General Eric Holder said in a statement.

Local authorities said the incidence of rape in Missoula, a western Montana city of 86,000 people, is on par with similarly sized college towns, and the county's chief prosecutor questioned the Justice Department's rationale for its inquiry.

The investigation comes in the midst of an election year in which women's issues have moved to the forefront as candidates seek to burnish their credentials among female voters.

'STRONG CONCERNS' AMONG WOMEN CITED

The Justice Department probe will examine the inner workings of the university's public safety office, the Missoula Police Department and the Missoula County Attorney's Office.

Additionally, the department will review whether the university is complying with federal laws specifically barring sex discrimination, defined as including sexual assault and sexual harassment, in education programs, officials said.

Details of the investigation were announced at a news conference in Missoula, whose economy and identity are closely entwined with the state's flagship research institution.

"There are a lot of women in the community who have strong concerns about the manner in which sexual assaults have been handled," said Assistant Attorney General Thomas Perez, head of the Justice Department's civil rights division.

The Justice Department said local law enforcement agencies in New Orleans, Puerto Rico and Maricopa County, Arizona, have been subjected to similar investigations.

Missoula Police Chief Mark Muir acknowledged his department had received roughly 80 rape reports in the past three years. But he said that on a per-capita basis, that figure was at or below the average level of reported rapes for U.S. college towns of similar size and makeup.

Muir, who said his department would cooperate with the inquiry, said he did not know how many of those reports had resulted in criminal charges being filed. Justice Department officials said they will be delving into that very question.

Missoula County's chief prosecutor, Fred Van Valkenburg, fiercely defended his office and the local police, calling the Justice Department probe an "overreach by the federal government."

"I have no reason to believe (police) violated anyone's rights," he said, adding that his office had no choice but to cooperate given "the heavy hand of a federal government that refuses to tell us what we supposedly have done wrong."

Concerns about the handling of sexual assaults in Missoula came to a head months ago at the University of Montana, a campus of some 15,600 students, after a spate of rapes were reported on campus, some involving student athletes.

A University of Montana report released in January identified nine alleged student-related sexual assaults or attempted assaults since late 2010, including a reported gang rape. Two more sexual assault allegations involving students have surfaced since then.

Criminal charges have been filed so far in just one of those 11 cases under scrutiny - against Grizzlies' running back Beau Donaldson, who is accused of raping a woman at his residence while she slept following a night of heavy drinking.

Donaldson, who has pleaded not guilty, has been suspended from the team.

The football team captain and quarterback Jordan Johnson was accused of rape in March and placed under a restraining order granted to his accuser. No charges have been brought and he, too, maintains his innocence.

(Reporting by Laura Zuckerman; Writing by Steve Gorman; Editing by Cynthia Johnston and Paul Simao)