SANTA CLARA, Calif. — The San Francisco 49ers have a new starting quarterback to protect over the second half of the season, and that's among several things they hope to get right over the next two months as they seek to rebound from a dismal 2-6 start.

The 49ers have allowed an NFL-high 34 sacks at midseason, and are on a pace to obliterate the franchise record of 55 allowed last season.

The inability to protect quarterback J.T. O'Sullivan was one of the team's glaring deficiencies during the five-game losing streak the 49ers take into Monday night's game against NFC West-leading Arizona.

O'Sullivan has now been replaced by veteran Shaun Hill, who will bring a different look to offensive coordinator Mike Martz's detailed system that has helped this year to lift the league's worst offense of 2007.

But that improvement has come at the expense of the quarterback, who so far has spent a lot of time on his back.

"That's definitely something were trying to get right," said Hill, who was sacked twice after taking over for O'Sullivan at halftime of San Francisco's last game, a 34-13 loss to Seattle on Oct. 26. O'Sullivan was sacked three times in the first half before departing the game in favor of Hill.

After Hill played well to finish that game, completing 15 of 23 passes for 173 yards during the second half in his first action of the season, coach Mike Singletary decided during the bye week to make the quarterback switch stick. Hill will make just his third NFL start Monday and his first on the road.

San Francisco's hopes of finishing strong will rely upon keeping Hill upright. The team's protection problems contributed to O'Sullivan fumbling 11 times — six of them lost — and throwing 11 interceptions in eight games. He leads the league with 17 turnovers, more than the total of 29 other NFL teams.

"That doesn't concern me," Hill said. "I guess when you're out there playing, you just go and play each play and you're not sitting there worried about that. You just kind of react to it."

Others have been worrying about it for Hill. The 49ers have made some recent personnel changes along their offensive line, which will have David Baas starting at left guard on Monday and Adam Snyder starting for the first time this season at right tackle.

The team also worked on some scheme modifications during the bye week to improve its pass protection.

"We've changed a couple of different techniques during the bye week to help eliminate (sacks), to try to get more help out to the tackles," said center Eric Heitmann, the veteran anchor of the team's line.

"As far as how we're playing as an offensive line, we just have to continue to protect as long as the quarterback needs us to," Heitmann continued. "Every week that's always a priority and something that as an offensive line you pride yourself on. The way our offense is run, there's a lot of opportunities for big plays and that constitutes having to hold onto the ball a little longer. So, as an offensive line, we've got to protect longer."

One of O'Sullivan's problems might have been that he held the ball too long in the pocket. That shouldn't be as much of an issue with Hill, who has a quick release and is likely to take shorter drops than O'Sullivan as Martz tailors the offense to suit Hill's strengths.

"I'm excited for the opportunity for Shaun and to see what he does with it," Martz said. "There's a lot of pieces around Shaun, or whoever's playing quarterback, that were trying to get settled. There are a lot of factors involved with those sacks, and I would not put them all on the offensive line. This is part of getting guys on the same page and fighting through this and we are pretty close to that, we really are."

HILL MOVES UP IN WR ROTATION

Arnaz Battle, San Francisco's leader among wideouts with 24 receptions, will miss Monday'0 game with a sprained foot. Second-year player Jason Hill will move into Battle's slot role in three-receiver formations.

Hill had an outstanding preseason during which he was second on the team with 11 receptions and averaged 18.5 yards per catch. But when the real games began in September, Hill found himself back on the bench, where he spent practically all of his rookie season last year.

Hill finally got an opportunity in the second half of the Seattle game after Battle was injured. He responded with three receptions — triple his previous career total including a 33-yard catch and his first career touchdown.

"You have to wait for your time," Hill said. "I thought I made some plays this preseason that would catch the eyes of the coaches faster. But that's just the way it goes in the NFL. You have to work through it and wait for your opportunity. Now, when my number is called, I just have to make sure I continue to make those plays, keep having fun, keep a smile on my face and stay confident and positive."

The 49ers are considering elevating receiver Dominique Zeigler from the practice squad this week. Zeigler, who has spent the past two years on San Francisco's developmental squad, has been impressive in practice since joining the team in the summer of 2007.

He also was one of the team stars of this summer, leading the 49ers with 15 preseason receptions. Zeigler has yet to make an appearance on the 49ers' 53-man roster.

Singletary said the 49ers would decide soon whether Zeigler will be making his NFL debut against the Cardinals.

"We'll see how he works out in the offense and if that's what were going to do," Singletary said. "We don't know yet what we want to do roster wise, but we'll figure it out."

EXTRA POINTS

OT Jonas Jennings, who has not played since being sidelined by a shoulder injury in Week 2, was limited in practice this week and was listed Friday as probable to return to action against the Cardinals. Singletary said Jennings would be ready to go if the 49ers needed him to play in a pinch. Battle, S Dashon Goldson (knee) and OT Barry Sims (ankle) are listed as out for Monday's game. DE Ray McDonald (knee) and TE Delanie Walker both practiced Thursday and are listed as probable. LB Roderick Green (illness) is questionable. The 49ers will have a lighter workout Saturday and then conduct meetings and a walk-thru practice Sunday before a charter flight to the Phoenix area.