San Francisco ? If the San Francisco 49ers hope to stay in the NFC West race, their quarterback change must work out just as well as the St. Louis Rams’ move did.

Jeff Garcia isn’t expected to play in today’s game against St. Louis. His sprained ankle got significantly worse during the week leading up to San Francisco’s biggest rivalry game, and team doctors ruled him out Thursday.

Tim Rattay is expected to make his first NFL start. If he needs inspiration from another backup quarterback who excelled in the spotlight, he could look across the field at Marc Bulger. Bulger claimed the starting job from two-time MVP Kurt Warner this season after getting his first chance as an injury replacement.

Nobody expects Rattay to duplicate Bulger’s achievements, but Rattay might be a breath of fresh air to an offense that has struggled all season.

“Tim doesn’t have to win it by himself — I mean, that’s the key,” coach Dennis Erickson said. “We’ve got other players on this team. Tim will do the things that he can do, and we’ll do what we’ll do. I think if you ask every player in that locker room, they’ve got confidence in Tim.”

But a change couldn’t hurt the 49ers. Just when they seemed ready to snap out of their funk after a 24-7 win over Tampa Bay two weeks ago, the Niners played abominably in a 16-13 overtime loss to lowly Arizona. And now Garcia can’t play against the surging Rams, whose brilliant offense is back in top form.

What’s more, the Rams expect running back Marshall Faulk to return after missing a month because of injuries.

Last season, the 49ers won the NFC West title and a trip to the second round of the playoffs, but they have regressed dismally this season under Erickson. San Francisco is 3-5, including a 27-24 overtime loss to the Rams in September.

The 49ers have problems everywhere, from a season-long kicking debacle to Terrell Owens’ repeated criticism of teammates. Erickson isn’t quite sure what to make of his inconsistent squad, which also seems to have a team morale lower than Garcia’s passer rating.

But Erickson might do well to emulate St. Louis coach Mike Martz, who had many of the same problems last season when the Rams slumped after reaching the Super Bowl.

“I know I was very hard on the team when we were losing,” Martz said. “Coaches get frustrated, but you have to identify what is going on. For us, we just weren’t doing the little things well. We weren’t playing with the pizazz and enthusiasm that was the trademark.”

St. Louis is 5-2 and back atop the standings with the NFC’s most prolific offense. The Rams have scored 203 points despite the absence of Faulk, who’s missed four games because of a broken hand and a sore knee.

“I would think he would be in a position to play quite a bit,” Martz said.