At Camp David, a movie theater and an airplane hangar have been outfitted with lights and production equipment to create a mock debate stage. At least 16 current and former aides, summoned from Washington and Wilmington, whiz back and forth on golf carts to join President Biden in strategy sessions.

Mr. Biden is entering his fifth day of preparations at the presidential retreat in the woods of northern Maryland for Thursday’s debate against Donald J. Trump. Camp David has become the epicenter for an administration and campaign effort to help Mr. Biden shake off the rust that often comes with being an incumbent on the defense, and combat widespread voter concerns that he is too old to be an effective president.

Both candidates are out of practice as debaters. And Mr. Biden’s top advisers, including Ron Klain, who is managing the debate preparations, are aware of the missteps incumbents have made in the past. In 2012, President Barack Obama flailed in his first re-election debate and had to quickly reorient for the second one.

So they will be working to position Mr. Biden not only as a president in the midst of a re-election campaign, but also as a fighter who can counterpunch on the fly. Mr. Trump, an opponent who is adept at extemporaneous insults, skipped the primary debates that could have sharpened his skills.

“The rust factor is real,” said David Axelrod, a former top strategist to Mr. Obama. “Neither of these guys is accustomed to having someone a few feet away, grilling them with no deference.”

According to people familiar with the planning at Camp David who were not authorized to speak publicly about it, the work days vary in length and are not rigidly structured. Mr. Biden and his most trusted advisers work on what they think would be best to refine or practice in the moment.

They are all trying to game out exactly which attacks Mr. Trump might launch at Mr. Biden, which policies of his Mr. Trump could try to undermine, and how they can best keep the president focused on landing an argument and striking a character and policy contrast with Mr. Trump.

Officials on Mr. Biden’s campaign believe that the debate will provide an opportunity to go on the offensive on issues like immigration and abortion access. In recent days, Mr. Biden has unveiled a program that would create new pathways to citizenship for people married to American citizens, while Mr. Trump has suggested that migrants form a league to fight one another. And this week marks two years since Roe v. Wade, which had guaranteed a constitutional right to abortion, was overturned by the Supreme Court.

Mr. Biden’s advisers say the setting itself will help highlight Mr. Trump’s weaknesses, and allow the president to combat the idea — presented in a slew of misleading videos — that he is bumbling in public. Mr. Biden and Mr. Trump will meet in a closed studio in Atlanta with no live audience. Each candidate’s microphone will be muted when it is not his turn to speak.

But it will still be live television, broadcast on CNN with moderators who will be under pressure to fact-check both men in real time but who have downplayed any expectation that they will wade into rebuttal territory. David Chalian, CNN’s political director, told The New York Times over the weekend that the moderators would focus on “facilitating the debate between these candidates, not being a participant in that debate.”

The Biden team will be doing everything it can to make sure there are no surprises.

Bob Bauer, Mr. Biden’s personal attorney, has played the role of Mr. Trump in mock debates at Camp David, just as he did in 2020.

In his book, “The Unraveling,” Mr. Bauer said he studied hours of tapes of Mr. Trump as a businessman, candidate and president before the 2020 debates. He wrote that he did not try to portray a “Saturday Night Live” version of Mr. Trump, with makeup and costumes. Instead, he wrote, “I used as much of the language he did on the topics that would come up in a debate.”

The actual Mr. Trump has engaged in something that resembles a more streamlined debate preparation process than in past years. He has sat for policy discussions with allies. But over the weekend, he said that he was relying on his experiences as a campaigner to guide him when he takes the stage across from Mr. Biden.

“Well, this is really the best strategy right here,” Mr. Trump told Fox News ahead of a rally in Philadelphia over the weekend. “We have all these people out here, and they are screaming questions. I look forward to the debate.”

At the rally, he attacked Mr. Biden for going “to a log cabin to ‘study,’” suggested Mr. Biden would be taking supplements to get “jacked up” before the debate, and said the president would spend most of his time at Camp David sleeping.

But Mr. Axelrod said the length Mr. Biden’s preparation was consistent with past presidents. He said Mr. Klain plans sparring and mock debates, which lead into a two- or three-day debate camp.

“Trump has a different process, in that he doesn’t believe in process,” Mr. Axelrod said. “What Biden is doing is more customary.”

Mr. Biden’s Camp David prep team includes Mr. Klain and Mike Donilon, who is the architect of the campaign’s theme that democracy is at stake if Mr. Trump wins. Steve Ricchetti, a counselor to the president who manages relationships on Capitol Hill, is also scheduled to be there, as is Jake Sullivan, Mr. Biden’s national security adviser.

Jeffrey D. Zients, Mr. Biden’s chief of staff, is expected to be there, as are aides focused on communications strategy, including Anita Dunn and Ben LaBolt, the White House communications director.

Several Biden campaign aides, including Jen O’Malley Dillon, Cedric Richmond, Julie Chavez Rodriguez, Quentin Fulks, Michael Tyler and Rob Flaherty, are also on the list of attendees.

Some are returning to the fold just long enough to help Mr. Biden prepare: Brian Deese, who left the administration as director of the National Economic Council in 2023, is expected to visit Camp David to help Mr. Biden refine his pitch that the American economy is recovering.

Several people said there will be a clear division between Mr. Biden’s inner circle and the diverse set of policy experts summoned to Camp David, some of whom are not expected to remain on site all week once the mock debates begin in earnest.

Annie Tomasini, Mr. Biden’s deputy chief of staff, is never far from his side. And Bruce Reed, a top policy aide to Mr. Biden, will be making a lot of the calls about which arguments need to be refined, according to people familiar with the planning.