The Saints had to find a one-season replacement for head coach Sean Payton, whose season-long suspension in connection with the bounty scandal begins Monday and runs through the next February's Super Bowl.
New Orleans general manager Mickey Loomis said in the release Thursday that Vitt will take over on Monday.
"It is important that we keep Sean Payton's philosophy front and center during this season," Loomis said Thursday. "Sean has been the driving force behind the tremendous success our team has enjoyed during the past six years, his leadership will be missed. But we need to set a course of action that gives us the best chance to win this season without our head coach. ... We considered a number of great options to handle Payton's duties both internally and externally, but believe this will provide the most seamless transition for our players and our coaching staff, allowing our offensive and defensive staffs to remain intact with the fewest changes.
"This is the same structure we used last season during Sean's knee injury."
Vitt, who carries the titles of assistant head coach and linebackers coach, briefly stepped in as interim head coach last season when Payton broke his leg. Vitt also was interim coach with St. Louis in 2005 before joining Payton in his first season with New Orleans in 2006.
Vitt will be able to oversee the offseason training program and training camp, before stepping aside for the first third of the regular season.
The NFL played no role in the decision-making process.
"It's the Saints' decision," NFL spokesman Greg Aiello said, adding the team did not have to get approval from the league to make Vitt the interim coach.
The Saints did not say what their plans will be during Vitt's six-game suspension.
"We will work through the offseason under this plan and when we get to training camp we will decide on a course of action for the first six weeks of the season, while Joe Vitt is unavailable," Loomis said. "We are fortunate to have a great veteran coaching staff well equipped to handle this challenge. Joe and Sean have worked closely together to build our program, one of the most successful in the NFL in the past six years, and I have the fullest confidence that Joe will continue that success that Sean has brought us."
The Saints' assistants who can pick up the slack during Vitt's absence include: offensive coordinator Pete Carmichael, offensive line coach Aaron Kromer and new defensive coordinator Steve Spagnuolo.
— Carmichael, who also joined the Saints in 2006, began calling plays after Payton's injury last season. Payton allowed Carmichael to continue calling plays through the final 10 regular season games of 2011 as the Saints went 9-1 and broke numerous NFL offensive records.
— Kromer, who also oversees the running game, will be entering his fifth season in New Orleans and like Carmichael has been mentioned as an up-and-coming head coaching candidate around the NFL.
— Spagnuolo, who was a head coach in St. Louis the past three seasons and defensive coordinator for the New York Giants' 2007-08 Super Bowl winning team.
The decision gives Saints players a measure of certainty and direction as Monday's first day of the offseason training program approaches.
Still looming, however, are possible punishments for between 22 and 27 current and former Saints defenders that the NFL says participated in the crunch-for-cash bounty system that disgraced former Saints defensive coordinator has apologized for running for the previous three seasons.
The league's investigation found that Williams' bounty system offered off-the-books cash payments of $1,500 for "knockouts," in which an opposing player was knocked out of a game, or $1,000 for "cart-offs," in which an opponent needed help off the field. The league has said the bounty pool grew as large as $50,000.
The investigation also found that Payton initially lied about the existence of a bounty program and instructed his defensive assistants to do the same.
Loomis received an eight-game suspension for failing to ensure the program was stopped after the NFL first asked him to do so in early 2010.
The franchise, meanwhile, was fined $500,000 and docked second-round draft choices this year and next, although NFL Commissioner Roger Goodell has said he may lessen the 2013 penalty by modifying which pick the Saints lose if the club cooperates with the NFL's ongoing probe.
Williams, who was hired as defensive coordinator in St. Louis after last season, has been suspended indefinitely. His penalty will be up for review after next season.