SAN JOSE — Until Thursday, Mario Enrique Cuestas stood out in the San Jose Fire Department for all the right reasons.

He was a leader within the rank-and-file and, as the department’s outreach director, its primary link to residents. He sang the national anthem at community events on multiple occasions, and also lent his voice to the Roman Catholic Diocese of San Jose.

Cuestas was confident enough to discuss publicly how in middle age he revealed to fellow firefighters he is gay, and how their acceptance helped fortify the department.

It’s why his arrest Thursday — on allegations that he was giving methamphetamine to and having sex with an underage teen — has been so earth-rattling for his colleagues and the greater community.

News of the arrest gradually spread at SJFD late Thursday, with many expressing confusion, anger and disappointment, Deputy Chief Robert Sapien said.

“The charges and the arrest are shocking to me and to all firefighters right now. Everyone feels horrible about that,” said Sapien, the president of the firefighters’ union. “To have that compounded by having a firefighter associated with those crimes is difficult. Clearly the behaviors are not in line with what we’re here to do, which is to help people.”

Agents from the Santa Clara County Specialized Enforcement Team — a state-run squad assembled from local police agencies — went to fire administration headquarters Thursday and quietly took Cuestas, 53, into custody before searching his office for evidence.

He was booked into the Santa Clara County jail and is being held without bail on suspicion of possessing and selling methamphetamine, providing narcotics to a minor, child molestation and oral copulation with a minor. He is being held in protective custody and declined a jail interview.

Friday morning, at Cuestas’ San Lorenzo home where he lives with his parents, his father, Mario Sr., said police came to his front door Thursday to inform him about the arrest and prospective charges.

“It came as a shock to us,” the father said.

He had little else to say beyond asserting he did not believe the allegations against his son, who has lived with him and his wife at the well-kept, single-story suburban home for about a year.

Cuestas has been with the fire department about 20 years, primarily as a fire engineer and driver and for some time as a fire investigator. He took on highly visible tasks, such as organizing Sept. 11, 2001 commemorations. In 2007 he helped lead an open-air drill at San Jose’s Municipal Stadium in which first responders trained for a potential biological weapon attack. He was also a volunteer for several causes and organizations, including a junior sports camp.

In October 2011, Cuestas appeared on an episode of “Outlook Video,” a gay, lesbian, bisexual and transgender monthly public access cable talk show, where he was one of three South Bay firefighters who discussed being openly gay.

Cuestas spoke about being accepted by his colleagues upon coming out. He also said he was previously married with children, including a son with aims to follow in his father’s firefighting footsteps.

“When I first came out it was a difficult step to take,” Cuestas said on the program. “It starts by looking at yourself in the mirror, whether at home or at work, and just realize this is who I am. I am gay. This is who I am and they have to accept me.”

His stature as a vocal, professional, hardworking firefighter eventually grew to a level where his support for local political candidates was touted in their lists of endorsements.

At the time of his arrest, Cuestas was settling into a new role heading the department’s office of public outreach, the liaison to schools and community and church organizations. Sapien said the behavior described in the criminal accusations “seems out of character for the person that we know.” But he said the bottom line “is the behaviors we saw described in the charges are completely unacceptable. We never want that kind of behavior related to anyone with the fire department.”

Sapien said he does not expect the firefighters’ union to fund a defense attorney for Cuestas, who has been placed on unpaid administrative leave.

A drug-related tip to the Santa Clara task force — which is overseen by the California Department of Justice — sparked a two-month investigation that ended with Cuestas’ arrest, DOJ spokeswoman Michelle Gregory said.

She added while Cuestas’ online activity was examined by agents, it does not appear he met his alleged victim, a 17-year-old boy, over the Internet. Agents conducted an undercover sting that bolstered allegations Cuestas gave meth to and engaged in sexual acts with the boy, Gregory said.

After his arrest, agents searched his office at the fire department where they confiscated a computer hard drive among other items. Gregory said they also searched his home. It was not immediately clear how Cuestas acquired the drugs.

Staff writer Natalie Alund contributed to this report. Contact Robert Salonga at rsalonga@mercurynews.com. Contact Mark Gomez at mgomez@mercurynews.com.