ST. LOUIS — By the time the 49ers plane touched down back home Sunday, the Mike Singletary era was over. Team president Jed York fired the head coach hours after the team was eliminated from playoff contention.

The final straw was a 25-17 loss in St. Louis, where the 49ers looked nothing like a team playing a must-win game. They were so flat and ill-prepared that York vowed a major shake-up even before the team headed home.

York’s final deliberation didn’t last long. At 9:04 p.m. on Sunday, the team released a statement saying that Singletary had been “relieved” of his head coaching duties.

“We should be a playoff team,” York said in the immediate aftermath of the loss. “We aren’t a playoff team this

year. I’m very disappointed about that. We need to figure out how we can get into the playoffs and how we can start to be a Super Bowl team again.”

Later, when the firing became official, York released a statement saying: “I want to thank Mike Singletary for the passion and effort that he brought to this organization. He is a tremendous person for whom I will always have great respect.”

Singletary went 18-22 after taking over as head coach midway through the 2008 season. Defensive line coach Jim Tomsula will serve as the interim head coach when the 49ers play their regular-season finale next Sunday against the Arizona Cardinals at Candlestick Park. Tomsula’s previous head coaching was with the Rhein Fire in NFL Europe.

The

49ers also will begin searching for a full-time replacement. A source said former Super Bowl winning coach Jon Gruden is high on the team’s wish list.

Firing Singletary is the start of more big changes to come. York, who had predicted a division title for the 49ers this season, sounded poised to embark on a major overhaul.

Most significantly, York said the 49ers would restore the position of general manager and said a search would begin soon. The new GM would play a role in the hiring of the next coach.

York also described quarterback as a position of need for 2011, indicating that the 49ers will part ways with free-agent-to-be Alex Smith after six seasons of unfulfilled promise.

“Our object is to win the Super Bowl, year in and year out,” York said. “We’re going to make sure we get this right.”

A consensus favorite in the division at the start of the season, the 49ers instead need a victory next Sunday just to avoid a last-place finish in the NFC West. Singletary’s fate was sealed with a mistake-filled loss to the Rams on Sunday, a defeat that included a shouting match between Singletary and starting his staring quarterback du jour, Troy Smith.

The game was ugly from the start. The 49ers botched a snap on each of their first two offensive possessions, went 4 of 16 on third-down chances and committed eight penalties for 87 yards.

“I mean, we come into a game like this and we look inept on offense in the first half. We didn’t get anything done except for two plays that, really, players made,” York said, referring to a 78-yard punt return by Ted Ginn Jr. and a 60-yard touchdown catch by Michael Crabtree.

“We aren’t where we need to be. I’m not taking anything away from the Rams. I’m not taking anything away from the Seahawks. I wish those teams the best of luck going forward. Somebody has to win the NFC West.

“(But) there’s no reason that we aren’t the team that won the division this year.”

Singletary’s fiery approach worked well in the immediate aftermath of the Mike Nolan tenure, but this year’s team has been marked by sloppiness, questionable play calling and a general sense of chaos.

No matter what changes Singletary made, including firing offensive coordinator Jimmy Raye after Week 3, the team continued to regress.

In a statement distributed through the 49ers’ media relations department, Singletary said: “I wish the 49ers nothing but the best. I am thankful to the York family for having given me the opportunity to be a head coach in the NFL. I am indebted to them for that. I am also thankful for the Faithful fans, I am just sorry I couldn’t give them more.”

The 49ers’ current front office lacks the general manager job title. Trent Baalke serves as the team’s vice president of player personnel, with Singletary having a major say over the 53-man roster.

York said there is no timetable for hiring a GM but added that the new executive would help him find a replacement for Singletary.

“We have enough talent that we should have been the NFC West champion,” he said. “We should have been competing in the playoffs.”