President Obama will correct a historical act of discrimination next month when he awards the Medal of Honor, the nation’s highest commendation for combat valor, to a group of Hispanic, Jewish and African-American veterans who were passed over because of their racial or ethnic backgrounds.

The unusual presentation will culminate a 12-year Pentagon review ordered by Congress into past discrimination in the ranks and will hold a particular poignancy when conducted by the nation’s first African-American president.

Although the review predates Obama’s tenure, he has made addressing discrimination in the military — including ending the ban on gay and lesbian service members — a priority as commander in chief.

With the ornate White House East Room as backdrop, the March 18 ceremony will mark another step to revisit a history of discrimination in the armed forces as the nation’s demographics and social values shift rapidly.

The recipients, whom the White House announced Friday afternoon, served in World War II, Korea, and Vietnam. Collectively, their award ceremony will mark the single largest group of Medal of Honor recipients since World War II, when more than two dozen service members were honored in that conflict’s last days.

Just three of the 24 veterans who will be honored are still alive. All but five of the soldiers are Hispanic, Jewish or African American, including Melvin Morris, a former Green Beret who was wounded three times on a mid-September day in 1969 recovering the body of his fatally wounded master sergeant from a jungle ambush in the Chi Lang district of South Vietnam.

“I never thought much about it and didn’t until recently,” said Morris, 72, who was decorated three times for his service in Vietnam and retired from the Army after 22 years. “But I think that this is something the military always should address because, in almost every process we have, someone is overlooked.”

The unusual historical accounting began in 2002 when Congress, as part of the military spending bill, ordered the Pentagon to look into whether Jewish and Hispanic service members had been passed over unfairly for the nation’s highest military honor.

Defense Department officials said there was specific evidence to suggest such discrimination may have existed in the ranks, including instances in which Hispanic and Jewish soldiers apparently changed their names to hide their ethnicity. The congressional order spanned the period from December 1941 through September 2001.

The project was an enormous undertaking that sent military personnel officials searching for lost records and battlefield histories amid the complicated politics surrounding the military’s highest honor.

Officials from each service branch focused on service members who had been awarded the second-highest medal for gallantry: the Distinguished Service Cross for the Army, the Air Force Cross for that branch, and the Navy Cross for the Navy and Marine Corps.

Although that narrowed the review, the Army alone identified more than 600 records that needed reassessment. The smaller branches found 275 among them.

“It’s hard to be awarded the medal for a single person, and to go back for all those potential candidates, that is a very demanding scope and record-retrieval task,” said a defense official who spoke on the condition of anonymity to comment on the review. “It was very time-consuming. But we wanted to make sure that, as a process, we did it correctly and that the Medal of Honor process itself was honored.”

Many of the veterans under review had passed away, making interviews impossible. Much of the review relied on existing information and comparisons to Medal of Honor recipients, but even then, there were challenges unforeseen when the project began.

In 1973, a fire tore through the National Personnel Records Center in St. Louis, destroying as many as 18 million military personnel files. Among those were Army service records from 1912 through 1960, a period that included World War II and Korea. The Air Force lost most of its personnel files from 1947 though 1964.

The disaster forced officials to recreate the military history of scores of potential candidates for the upgraded commendation by interviewing family members, fellow battlefield soldiers, and others.

The reassessment sent a host of candidates through the various service boards that decide on Medal of Honor recipients and then to the Joint Chiefs for approval. Two dozen veterans — all from the Army — emerged as worthy of an upgrade to the Medal of Honor.

They include 17 Hispanic soldiers such as Santiago J. Erevia, a former specialist four who served in Vietnam as a radio telephone operator in Company C, 1st Battalion (Airmobile), 501st Infantry of the 101st Airborne Division. He will receive the Medal of Honor at the March 18 ceremony for “courageous actions” during a search-and-clear mission near Tam Ky, Vietnam.

“We’ve wondered why he didn’t receive it the first time and thought it may have been because of his name,” said Jesse Erevia, 41, his son, who lives in San Antonio, not far from his father.

Erevia said his father had “some issues” with the Vietnam War, mainly concerning its rationale, and has mixed feelings about military honors in general. But the family is eager to attend the White House ceremony next month to see him receive an award they have long felt he deserved.

“He’s never let me down,” Erevia, a tamale salesman, said of his father. “His are big shoes to fill.”

The third living veteran is Jose Rodela, a former sergeant first class from Corpus Christi, Tex., who will receive the medal for bravery during fighting in Phuoc Long province, Vietnam, in early September 1969.

The review identified one deceased Jewish veteran, former Pfc. Leonard M. Kravitz, to receive the Medal of Honor.

In early March 1951, Kravitz was serving as an assistant machine gunner with Company M, 5th Infantry Regiment of the 24th Infantry Division. His actions in combat over two days in Yangpyong, Korea, were deemed worthy of the highest honor.

“In this instance, justice was delayed but not denied,” Abraham H. Foxman, national director of the Anti-Defamation League, said Friday in a statement.

Morris was the only African-American veteran identified as part of the review. The initial congressional order did not include black service members for reassessment, but it was later amended to allow others deserving an upgraded commendation — not just Hispanic or Jewish service members — to receive one.

Of the two dozen soldiers in the White House announcement, five identified themselves on military personnel forms as “Caucasian.” Military officials said their ethnicity or religious affiliation is uncertain, but their battlefield actions were found to deserve the highest honor.

Morris grew up in small-town Oklahoma, the son of a “do-it-all carpenter” and a housemaid. He joined the Army because at the time, he recalled, “it was the prestigious thing to do, and if you got in, you went.”

As part of a Special Forces A Team carrying out search-and-destroy missions with local Montagnard troops, Morris was ambushed on Sept. 17, 1969, on a jungle patrol. His company commander was shot through the mouth and throat, his operations sergeant was severely wounded by a land mine and his master sergeant, Ronald P. Hague, was killed.

“We were a tight crew and we didn’t leave anyone behind,” Morris said. He took soldiers to retrieve Hague’s body three times before succeeding. He said last rites over his friend and then was shot through the chest, the arm, and the ring finger — tearing it off along with his wedding band.

After recuperating in a stateside hospital, Morris returned to Vietnam for another tour, this time as the recipient of the Distinguished Service Cross. “I never thought about the medal, whether it should have been another higher one,” he said. “I just kept doing what I was doing.”

Morris said he did not consider whether his race played a part in the commendation selection. He was not blind to race; Morris recalled being unable to use the public drinking fountain outside the Southern base where he trained for Special Forces.

“This is wonderful,” he said. “I’m overwhelmed. And there are more out there.”

Morris said he will travel from his Florida home to the White House next month with his three children and his wife of more than five decades, Mary, who gave him the ring that was shot off with his finger that day in Vietnam.

“I haven’t worn one since,” he said.

Alice R. Crites contributed to this report.