SANTA CLARA – Coach Jim Harbaugh waited until game time two weeks ago to anoint Colin Kaepernick as the 49ers' starting quarterback and until Wednesday to do the same last week. This time, he's not letting the uncertainty linger.

Harbaugh said Monday he doesn't foresee making a quarterback change this week, leaving Kaepernick in line to start against Miami after the second-year player absorbed his first defeat as an NFL starter in a 16-13 overtime loss to St. Louis on Sunday.

Kaepernick completed 21 of 32 passes for 208 yards and rushed for 84 yards on nine carries in the loss. He also was at the center of two mistakes that loomed large in hindsight – a disputed safety and a botched option pitch to Ted Ginn that the Rams recovered for a pivotal touchdown.

"There were a lot of positives in the game," Harbaugh said. "Specifically with Colin, I thought especially after the fumble touchdown, the way he responded, the way our team responded again putting ourselves in a position to win after that … he responded with some big throws and some big plays."

Harbaugh said he isn't tempering his expectations of Kaepernick because of his inexperience. Harbaugh also was asked if the decision to start Kaepernick, who has completed 66.3 percent of his passes for 682 yards in three starts, comes partly from wanting to accelerate the young quarterback's growth.

"I think the biggest thing is what helps us win now, these games that we've played and going forward," Harbaugh said.

Sunday would be the fourth consecutive start for Kaepernick, an indication his claim to the job may be strengthening. Yet Harbaugh was careful not to close the door on Alex Smith, who completed 70 percent of his throws and had the 49ers at 6-2 before suffering a concussion Nov. 11.

"Alex is not out of this," Harbaugh said. "He's one of our guys; he's won us a lot of football games. And he'll be preparing himself to play in each of these games every single week. That's what his mindset needs to be, as if he was the starting quarterback.

"That's what we expect, and if I know Alex, that's what he'll do."

A subdued Harbaugh spent much of his news conference taking responsibility for the failed option pitch – a risky play from the 49ers' 17-yard line with an eight-point lead and 3:11 to play.

Harbaugh said he could have overruled the call by offensive coordinator Greg Roman. Kaepernick, who said he could have held the ball under pressure, made an off-target flip, and Ginn couldn't scoop up the ball in what Harbaugh called "the nightmare scenario."

It is incumbent on the 49ers, who lead the NFC West by 1 1/2-games, to close out games where they have a late lead and the defense plays "near-perfect," Harbaugh said.

"We're in a position to control our own destiny and bounce back," he said. "There might be certainly a bit of an edge, I would expect, because we all take responsibility that we didn't get it done this past week."

Et cetera – Harbaugh said he expects David Akers, who has been battling a pelvis injury, to kick for the 49ers on Sunday against the Dolphins but that the team will "see what his health status is this week." Akers missed a potential game-winning 51-yard attempt in overtime against the Rams.

• Harbaugh did not provide an update on wide receiver Mario Manningham, who left Sunday's game in the fourth quarter with an injury. He already had been on the team's injury report because of a sore right shoulder.

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