Military recruiters across the country have been caught in a string of sex-crime scandals over the past year, exposing another long-standing problem for the Defense Department as it grapples with a crisis of sexual assault in the ranks.

In Alaska, law enforcement officials are fuming after a military jury this month convicted a ­Marine Corps recruiter of ­first-degree sexual assault in the rape of a 23-year-old female civilian but did not sentence him to prison.

In Texas, an Air Force recruiter will face a military court next month on charges of rape, forcible sodomy and other crimes involving 18 young women he tried to enlist over a three-year period. Air Force officials have described the case as perhaps the worst involving one of its recruiters.

In Maryland, Army officials are puzzling over a murder-suicide last month, when a staff sergeant, Adam Arndt, killed himself after he fatally shot Michelle Miller, a 17-year-old Germantown girl whom he had been recruiting for the Army Reserve. Officials suspect the two were romantically involved, something expressly forbidden by military rules.

Leaders of the armed services said they place enormous emphasis on ethical behavior and professional conduct when selecting and training recruiters, who are a fixture in high schools everywhere and critical to the nation’s all-volunteer military. Only a tiny percentage of recruiters engage in sexual misconduct, officials said, and there is no tolerance for those who do.

The extent of the problem is hard to ascertain because the Defense Department does not keep figures on recruiters accused of sex crimes. The Army, Navy, Air Force and Marine Corps track incidents separately, but there is no uniform standard, which makes statistical comparisons difficult.

In most cases, the victims are teenagers or young adults who have expressed an interest in a military career but have not yet enlisted. As a result, they are excluded from Pentagon surveys that show an alarming rise in the number of active-duty military personnel who say they have been sexually assaulted.

“Anecdotally, we absolutely hear that this is a problem,” said Anu Bhagwati, a former Marine captain who is executive director of the Service Women’s Action Network, an advocacy group. “There certainly is a power dynamic there that makes it a target-rich environment for a predator.”

In response to an outcry from the public, lawmakers and the White House, Defense Secretary Chuck Hagel last week announced several initiatives to prevent sexual abuse and impose accountability for commanders who do not take the problem seriously. Hagel included a directive to “improve the effectiveness” of sexual-assault prevention and response programs in the armed services’ recruiting commands, though the Pentagon did not provide details.

“The secretary has made it clear that we will spare no effort to rid our military of sexual abuse,” said George Little, the Pentagon press secretary. “The fact that there have been problems of sexual abuse during the recruiting process is simply intolerable.”

Strict rules violated

In several cases over the past year, recruiters have been charged with or convicted of having sex with underage girls whom they were trying to recruit, despite strict rules against fraternization or even spending time alone with youths of high school age.

In Oregon, an Army staff sergeant pleaded guilty in March to having sex with a 17-year-old girl in a recruiting office. In Arizona, an Army staff sergeant was charged in November with having a sexual relationship with a minor after he allegedly took a 16-year-old student to a park on multiple occasions and exchanged nude photos with her.

In Oklahoma, an Air Force staff sergeant was convicted of dereliction of duty by a military court in November after he had sex with a recruit, in a relationship that began with sexually explicit text messages.

Around the same time, officials with the Air Force Recruiting Service said they redoubled their efforts to ensure that recruiters don’t cross the line. The impetus was a sex scandal at the Air Force’s basic-training school at Lackland Air Force Base in Texas, where more than 30 instructors have been investigated on suspicion of abusing or mistreating recruits.

The Air Force has since required recruiters to undergo “enhanced” and more frequent training, “just a constant reminder of what’s acceptable,” said Col. Michael Vlk, vice commander of the recruiting service, headquartered at Randolph Air Force Base in Texas.

Potential recruits also are required to watch a video and sign documents that spell out the boundaries of professional behavior. “What might be acceptable in the civilian world is not in the military world, for example, flirting or sexting,” Vlk said.

Since 2008, the Air Force has court-martialed an average of four recruiters a year for sexual misconduct or unprofessional relationships, officials said. A smaller number received lesser forms of discipline.

Misconduct redefined

The Army Recruiting Command, based at Fort Knox, Ky., has recorded a far higher number of sexual misconduct cases. Over the past five years, 387 incidents were investigated. Of those, 327 were “substantiated,” said Lt. Col. S. Justin Platt, an Army spokesman at the Pentagon. The Army has about 10,800 recruiters, by far the most of any of the armed services.

The Army expanded its definition of misconduct in 2011 to include such transgressions as sending inappropriate text messages to recruits or failing to observe the Army’s new “buddy system,” which requires two recruiters to be together at all times in the presence of an applicant of the opposite sex.

The Army did not provide an annual breakdown for its sexual misconduct figures. Platt said allegations have dropped since the service adopted the buddy system and began stricter screening of recruiters last year.

Of the Navy’s 6,200 recruiters, two dozen have been accused of sexual assault since 2010, according to the Navy Recruiting Command in Millington, Tenn., which did not provide further details. The Marine Corps Recruiting Command at Quantico, Va., did not provide figures, though a Marine spokesman said the number of recruiters who are found guilty each year of sexual assault or nonconsensual sex was in “the single digits.”

The Marine Corps adopted a “campaign plan” in December to refine and improve its sexual-assault prevention programs. Steve Wittle, deputy operations officer for the recruiting command, said recruiters have always been heavily exposed to ethics training but that more emphasis has been given to sexual assault in recent years.

In Alaska, however, civilian authorities are questioning whether the Marine Corps takes sex crimes seriously enough.

On May 3, a military court convicted Marine Gunnery Sgt. Nicholas Howard, 33, of ­first-degree sexual assault and adultery in the rape of a 23-year-old woman during a get-together with friends at his Anchorage home. Howard was sentenced to a dishonorable discharge but was not given any jail time.

Alaska law enforcement officials ceded jurisdiction to the Marine Corps after military investigators offered to speed up crime-lab testing of a DNA sample that became crucial evidence in the case. Two Anchorage police detectives and a forensic nurse testified against Howard during his court-martial and said they were stunned by the light sentence.

“The outcome was certainly a surprise to us,” said John B. Skidmore, chief of the criminal division for the Alaska Attorney General’s Office. “For almost any sexual assault case that is prosecuted in the state of Alaska, there is an expectation that there will be some jail time associated with it.”

Skidmore said his office was reviewing the case to determine whether state authorities would press their own charges against the Marine recruiter. “We attempt to prosecute these cases fairly aggressively,” he said.