The next day, Frank Gore fresh off a 153-yard rushing performance against the Broncos announced he would go after Eric Dickerson's single-season rushing record when the new season began. Coach Mike Nolan said he expected his team would make the playoffs, something the 49ers had not done since 2002.

His players enthusiastically agreed. They'd shown they could win big games on the road. They had a Pro Bowl running back, an up-and-coming quarterback and a defense that would benefit greatly from a free-agency spending spree. The expectations only grew from there.

Fast forward 10 months and the 49ers are as far away from their postseason goals as Gore is from catching Dickerson. With 435 yards through the first half of the season — 26th in the league — Gore would need to average more than 208 yards a game to claim the record.

Gore, who missed Sunday's game with a sprained ankle, hasn't had a 100-yard rushing day since the Broncos game. Indeed, one of the hardest things to comprehend about the 49ers is why the running game, which was one of the league's best last season and the backbone of the San Francisco offense, nearly has vanished this year.

The 49ers began the season with virtually the same offensive line they had in 2006. The only difference was at right tackle, where first-round draft pick Joe Staley has been by all accounts an upgrade over predecessor Kwame Harris.

The midseason will bring changes.

Nolan yesterday said left tackle Jonas Jennings, who missed the past two games with a high-ankle sprain, will have surgery on that ankle and go on injured reserve. Adam Snyder likely will start for the rest of the season.

Jennings was Nolan's first big acquisition as head coach, and the 49ers used a seven-year, $36million contract to snag him. Jennings, however, has played in just 21 of 40 games since joining the 49ers. He missed one game this season because of a "private matter" on which he has he has declined to comment.

Right guard Justin Smiley also looks as if he'll be out for at least the near future. Smiley severely dislocated his right arm while recovering a fumble in Sunday's loss to the Falcons and wore a sling Monday. Smiley played through a torn labrum in his opposite shoulder last year but said the new injury — a tear to his right labrum — was more severe. He will fly to Birmingham, Ala., to visit with Dr. James Andrews today, and season-ending surgery is an option.

David Baas, the team's second-round pick in 2005, filled in for Smiley in Atlanta and will do so until he returns.

Gore, meanwhile, is expected back for the 49ers' next game Monday night in Seattle. His success will depend as much upon quarterback Alex Smith as it does his new offensive line.

Smith struggled in Atlanta, finishing with three interceptions, a fumble and a 22.8 passer rating. On a weekend in which one NFL quarterback threw for more than 400 yards and five others surpassed 300 yards, Smith threw for 149. He has surpassed the 200-yard barrier only once this season and has yet to have a 300-yard game in his career.

Smith would not blame his performance on his still-mending right shoulder, instead concentrating on three potentially game-changing completions he either overthrew or threw out of bounds.

"Those are the plays you rewind and rewind," Smith said.

But the quarterback also touched on perhaps the 49ers biggest reason for optimism: that none of the teams in the NFC West have a positive report card through the season's first half.

The division leader, Seattle, lost in overtime Sunday and is 4-4 heading into Monday night's game with San Francisco.