Army Pfc. Bradley Manning said Thursday that he will live as a woman and seek hormone replacement therapy while incarcerated, confronting the military prison system with a demand that has prompted state and federal institutions to reluctantly offer similar treatment to inmates.

“I am Chelsea Manning. I am a female,” the former intelligence analyst wrote in a statement released on NBC’s “Today” show just a day after he was sentenced to 35 years at the U.S. Disciplinary Barracks at Fort Leavenworth, Kan., for leaking classified documents.

The Army issued a statement saying that Manning will receive counseling from mental health professionals at the all-male prison but that the Army does not “provide hormone therapy or sex-reassignment surgery for gender identity disorder.”

Manning’s attorney, David Coombs, was equally adamant that he will try to change that policy, foreshadowing another legal battle between a transgender person and a prison bureaucracy. With Manning’s profile already sky-high as a result of his conviction and sentencing, the conflict seems likely to keep the 25-year-old in the public eye for some time.

Manning’s statement wasn’t a complete surprise. Four hours of testimony in the sentencing portion of the soldier’s trial were devoted to mental health issues, including his struggle with gender dysphoria, as the condition is known. Manning received the diagnosis in May 2010, shortly before he was arrested in connection with transmitting hundreds of thousands of classified documents to the organization WikiLeaks.

Still, Manning’s statement that “I am Chelsea Manning… I also request that, starting today, you refer to me by my new name and use the feminine pronoun” was unexpected.

“Private Manning is facing 35 years in prison and needs to make a decision about what she’s going to be doing for all those years,” said Mara Keisling, executive director of the National Center for Transgender Equality. With parole eligibility seven years away, “now is a pretty good time for Private Manning to determine what she’s going to do for that period of time, what kind of person she’s going to be.”

Greg Rinckey, a former Army judge advocate general, said he expects the Pentagon to “take the position that Private Manning is still male. He still has a penis and hasn’t gone through surgery. If he fears for his safety, he can be put in isolation or protective custody.”

Rinckey said he thinks Manning’s attorneys are trying to get him transferred from Fort Leavenworth to a federal prison. “The military has the ability to do that,” he said. “It is rare, but it can happen.”

The impact on public opinion of Manning’s announcement is difficult to predict because his decision to leak classified information was already controversial, said Amy Stone, a sociology and anthropology professor at Trinity University in San Antonio. But Manning’s familiarity to many Americans could help promote greater acceptance of transgender people, she said.

“Whenever someone we know comes out as gay, lesbian or transgender, it impacts us differently than it does when we don’t know them at all,” she said. “There was a lot of invisibility around transgender issues in the past.”

In recent years, a federal judge has ordered Massachusetts corrections officials to arrange an inmate’s sex change operation and federal prisons were forced by a lawsuit to offer hormone therapy to prisoners even if they were not receiving it before incarceration.

The Constitution’s Eighth Amendment guarantees prisoners humane treatment, including the right to adequate medical treatment, U.S. District Judge Mark L. Wolf wrote in 2012, when he ordered the state of Massachusetts to provide Michelle Kosilek with sex-reassignment surgery. The protections apply to military prisoners as well. The state has appealed the decision.

“Our detention facilities have to provide a basic level of health care,” said Chris Daley, deputy executive director of Just Detention International. “That’s a constitutional right that everybody has.

“Beyond that, it’s just good management,” he added.

Other states, however, do not offer the surgery or other forms of treatment to transgender people. A 2011 report by the National Gay and Lesbian Task Force and the National Center for Transgender Equality said that 16 percent of men transitioning to women in jail or prison reported that they were denied regular health care and that 24 percent said they were denied hormones.

Federal prisons, which had offered hormone therapy only to people who were receiving it before confinement, were forced to change their “freeze frame” policy in a 2011 settlement of a case brought by inmate Vanessa Adams. U.S. prisons now offer evaluation and treatment to anyone with gender dysphoria, even if it is diagnosed in prison.

The condition affects people whose sex at birth is contrary to the one they identify with, according to the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, the bible of psychiatric diagnoses. Capt. David Moulton, a military forensic psychiatrist who examined Manning for the defense, said the soldier has had symptoms of the disorder since childhood. While on leave in January 2010, Manning spent a good deal of time living as a woman. He took a photo of himself dressed as a woman that he eventually sent to an Army superior.

There is little data on the number of transgender people in U.S. prisons. A survey of the 160,000 inmates in California identified 330 transgender prisoners. Similarly, it is difficult to estimate the number of transgender people in the U.S. population, advocates said.

But they also said that people who feel trapped in the wrong body are overrepresented in the prison population, where they face harsh conditions. According to the 2011 report, 38 percent of black transgender women reported that they were sexually assaulted while incarcerated.

Transgender people also are overrepresented in the military, with 20 percent of those surveyed saying they have served, Keisling said.

Marci L. Bowers, a California-based gynecologist and surgeon who has performed about 1,100 male-to-female surgeries over the past decade, said many of her patients report having wrestled with gender issues for most of their lives and joined the military as part of an effort to conform to society by seeking a “macho” environment. She said some also acknowledged having secretly hoped that they would die at war, allowing them to avoid their gender issues and bring honor to their families, only to discover after surviving deployment that gender reassignment didn’t seem as daunting as before.

“It’s like, ‘I survived a combat mission to Afghanistan, with bullets and IEDs. How much worse could this be?’ ” Bowers said. “They realize they don’t have anything to lose.”

Hormone therapy can take years to produce its ultimate effects, experts said, although continuous doses will result in changes such as softer skin, fat and muscle rebalancing and breast development in the first few months. Those changes begin to become irreversible in six to nine months. The younger a patient is when he starts to take hormones, the better they work, said Grace Kim, a D.C.-based psychologist with a number of transgender patients.

Brady Dennis, Juliet Eilperin, Meeri Kim and Sandhya Somashekhar contributed to this report.