Attorney General Jeff Sessions may have declined calls to appoint a second special counsel to investigate the FBI’s behavior during the 2016 campaign, but the man he has picked to lead an internal Justice Department review is a special counsel in every way but name.

John W. Huber, the U.S. attorney in Utah, can convene a grand jury, issue subpoenas, collect evidence and order witnesses to testify — all the usual powers a federal prosecutor has — as he delves into whether the FBI abused its powers when it sought permission and then carried out wiretapping of a Trump campaign figure, or whether it trod too lightly in pursuing questions about Democratic presidential candidate Hillary Clinton.

Mr. Sessions said the facts of the FBI situation don’t yet rise to the level of demanding a special counsel, but Mr. Huber is as close as can be.

“He will have the full authority of a federal prosecutor,” said Richard Painter, former chief ethics attorney for President George W. Bush. “If he looks at this and finds someone in the DOJ lied to a government official, he would be able to convene a grand jury, compel testimony and even prosecute them.”

By appointing an active federal prosecutor — in this case one first nominated by President Obama and kept on by President Trump — Mr. Sessions also may deflect criticism that the review is a partisan attempt to undermine the other special counsel, Robert Mueller, who is investigating the Trump campaign’s interactions with Russia in 2016.

Paul G. Cassell, a former federal judge who has known Mr. Huber since law school, said asking an acting U.S. attorney to lead the investigation is a good move because it may tamp down on excesses.

“When you have a special counsel, you always have to wonder if there is overzealousness in their prosecution because they only have one case,” he said. “Huber is going to be less inclined to move forward with prosecution unless it’s warranted because if he moves one case forward, others will be left behind.”

Questions remain about how Mr. Huber will operate. The Justice Department declined to comment on whether he will have a budget or appoint a team like Mr. Mueller. It also would not discuss how Mr. Huber’s probe would work with other active investigations, including Mr. Mueller’s.

“If he starts digging into the [Foreign Intelligence Surveillance Act] warrant, for example, he may find something really ugly,” Mr. Painter said. “But some of that may need to be handed over to Mueller.”

Justice Department Inspector General Michael Horowitz has launched an investigation similar to Mr. Huber‘s. It is not clear, however, if Mr. Horowitz’s reach can compel testimony from key players who are no longer in the federal government, such as former FBI Deputy Director Andrew McCabe.

Mr. Sessions fired Mr. McCabe last month on charges of misleading investigators looking into whether the bureau slow-walked its investigation into Mrs. Clinton’s exclusive use of a private email server as secretary of state.

Mr. Huber is said to have the power to force testimony from people who have exited the government.

Some Republicans who have demanded a second special counsel expressed support for Mr. Huber. Sen. Mike Lee, a Republican from Mr. Huber’s home state of Utah, called him a “capable public servant and a man of great integrity.”

Insider or outsider?

Those who know Mr. Huber describe him as a humble man who flies coach. They also praise his character, fairness and ability to handle high-profile cases.

Whether he is ready for the spotlight of the FBI investigation, though, remains to be seen. He could face accusations of partisanship from Democrats or become a target for Mr. Trump’s Twitter outrage, as have Mr. Sessions, Mr. Mueller and others.

“I don’t think John has anything in his background that gets you ready for something like this,” said former U.S. Attorney Brett Tolman of Utah, who spent four years in Washington as chief counsel for the Senate Judiciary Committee and recruited Mr. Huber to the U.S. attorney’s office.

“My time on the Judiciary Committee was high-profile, and it was a rude awakening coming to D.C. from the U.S. attorney’s office, where everything is black-and-white and not bogged down by politics,” Mr. Tolman said.

Others say the fact that Mr. Huber comes into the job encumbered with political baggage will be an asset.

“He’s a real guy, not a phony, and that is so important in Washington,” said Tom Gorman, director of the Rocky Mountain High Intensity Drug Trafficking Area, an anti-drug task force that Mr. Huber once chaired. “I know D.C. is different, but he’s very secure in himself and even as U.S. attorney he knows he is going to take a lot of heat from people.”

Mr. Huber has some experience in the Washington spotlight.

Last year, he appeared at a White House press briefing to voice support for two bills that would impose tougher penalties on illegal immigrants. The appearance raised questions for some about the Justice Department’s independence from the White House.

After the White House briefing, Mr. Huber took a leadership position on the Justice Department’s advisory committee of U.S. attorneys, which offers insight and advice to Mr. Sessions. But he was first appointed to that committee by Mr. Obama’s last attorney general, Loretta E. Lynch.

“John has been favorite of Sessions,” Mr. Tolman said. “I’ve never seen a U.S. attorney give a press conference from the White House on a controversial topic before, which John did. This appears to be some effort by Sessions to have someone in the trenches that he considers one of his own.”

Bipartisan support

Mr. Huber has received high marks from Republican and Democratic administrations. In 2004, Attorney General John Ashcroft honored him for his work fighting violent crime. In 2010, Attorney General Eric H. Holder Jr. recognized him for his performance as a federal prosecutor.

Appointed as U.S. attorney by Mr. Obama in 2015, Mr. Huber resigned when Mr. Trump took office, as is the custom when there is a turnover in administrations. But Mr. Trump renominated Mr. Huber last year, and the Senate confirmed him for another four years.

A native of Magna, Utah, Mr. Huber got his start prosecuting routine crimes such as domestic violence in Weber County, an area so conservative that Bill Clinton finished fourth there in the 1992 presidential election. As a county prosecutor, Mr. Huber garnered some attention for his success in handling gun crimes at the state and federal level.

That success led to the U.S. attorney’s office, where he continued prosecuting gun cases. Perhaps his most high-profile case was the 2008 prosecution of a man who sold a gun used in a mass shooting at a Salt Lake City shopping mall. The shooting and trial generated national headlines.

“The case was very complicated because it involved the prosecution of an illegal firearm acquisition by the shooter,” Mr. Cassell said. “Huber navigated the issue in a way that brought credit to the office and received nearly universal praise for how it was handled. He showed great concerns for victims.”

During his college days, Mr. Huber played football for legendary University of Utah coach Ron McBride, who taught him to “be the hammer, not the nail,” according to an article in the Salt Lake City Deseret News. His colleagues say he still lives by that motto.

“John is a very ethical man,” Mr. Gorman said. “He won’t be swayed by anything other than doing the right thing. If Sessions picked him, then my hat is off to Sessions.”