SANTA CLARA, Calif. — Mike Singletary replaced his coaching mentor Tuesday with a vow to build on what Mike Nolan started with the San Francisco 49ers.

Singletary acknowledged mixed feelings when the 49ers asked him to be the interim successor to Nolan, the dapper coach whose teams never played as well as he dressed. Nolan was fired Monday night after seven games in his fourth consecutive dismal season.

Singletary, the former linebacker who made the Hall of Fame during his stellar career with the Chicago Bears, praised Nolan's work in raising the 49ers to a measure of respectability after they arrived in town nearly four years ago to take over the NFL's worst team. After accepting the job with Nolan's blessing, Singletary said he thinks San Francisco can improve quickly.

"Right now, the guys realize that we do have something here," Singletary said. "To what degree, I don't know, but we do have something special here. It's a matter of stepping in and being able to bring it together, and that's something I've done all my life."

After four straight losses culminating in Sunday's 29-17 defeat to the New York Giants, the 49ers didn't even wait until their bye next week before replacing Nolan with Singletary, who has been Nolan's right-hand man since he entered coaching in 2003. Singletary also will be a candidate for the permanent job after the season, general manager Scot McCloughan said.

"I don't think there's one right time for a decision like this," McCloughan said Tuesday. "If you go off past experience and talking to people, the bye week is usually the best for this, but I think with the distractions on the outside, the most important thing this week is for us to be ready for the Seahawks."

The 49ers also fired offensive line coach George Warhop, one of Nolan's original assistants. San Francisco has yielded a league-high 29 sacks this season.

Nolan cut a striking figure on the 49ers' sideline in his custom-made dress suits and ties. His team's performances, however, could not match his sartorial splendor. He was 18-37 in nearly 3½ seasons with the 49ers, who hired the veteran defensive coordinator to run every aspect of the club in January 2005.

Nolan restored competence to a franchise that finished with the NFL's worst record in 2004, but he has the lowest winning percentage (.327) among any San Francisco coaches who made it through more than one season with the team. He barely avoided dismissal after finishing 5-11 last season, but couldn't even make it to midseason this fall.

Instead of logically delaying a decision on Nolan's fate until the bye following Sunday's home game against Seattle, McCloughan and owners John and Jed York suddenly couldn't wait another day to get rid of the family's choice to fix the 49ers, who have endured five consecutive losing seasons and haven't made the playoffs since 2002.

"In 2005, Mike Nolan took over a bad football team," Jed York said. "Mike (Nolan) and I have gotten to be pretty close. This obviously was not an easy decision to make, but this was about what happens on the field. Mike made this place better, he made me better, but unfortunately, this didn't translate into victories. I'm very excited to see what Mike can do and bring out the passion and intensity in our football players."

Nolan was the third NFL coach to be dismissed during the season, joining Oakland's Lane Kiffin and St. Louis' Scott Linehan. The Rams have won two straight games under interim coach Jim Haslett, and the Raiders are 1-1 under Tom Cable.

Singletary, the famed centerpiece of the Chicago Bears' dominant defense during the 1985 season on their Super Bowl team, has been at Nolan's side since 2003, when he worked for Nolan on the Baltimore Ravens' coaching staff. Singletary interviewed for a handful of head coaching vacancies in recent years, but was out of the NFL from the end of his playing career in 1992 until joining the Ravens.

The 49ers fielded the NFL's worst offense during two of Nolan's first three seasons, including last year. His first two offensive coordinators — Mike McCarthy and Norv Turner — left after one season for head coaching jobs, and Mike Martz became his fourth offensive coordinator last winter.

Nolan's future also was heavily tied to quarterback Alex Smith, the No. 1 overall pick in 2005. Smith never became a consistent starter in his first three seasons, and had an embarrassing public spat with Nolan last year over the severity of the quarterback's shoulder injuries, which forced him onto injured reserve.

Smith's shoulder gave him more problems this year, and the quarterback went on injured reserve before the season began. The 49ers promoted veteran journeyman J.T. O'Sullivan to the starting job, but a decent offense under Martz's direction hasn't been able to counteract a defense that has yielded a league-high 196 points.