The San Francisco 49ers are unsettled on defense, and first-round draft pick Aldon Smith is ready to take advantage of the opportunity to make an early impression.



The 49ers conducted their first padded training camp practice Sunday without five of their regular defensive starters from last season, and Smith is hoping he can have an immediate impact on a team that has been searching for a pass rusher since former Cal standout Andre Carter left town.



“I’m excited and it’s definitely a chance for me to step up and maybe fill the gap for whoever’s not here,” the outside linebacker said.



Linebacker Takeo Spikes left in free agency, and cornerback Nate Clements was released Friday because of his exorbitant contract. Linebacker Manny Lawson, nose tackle Aubrayo Franklin and free safety Dashon Goldson each are testing the open market as unrestricted free agents.



The 49ers don’t expect to re-sign Franklin or Lawson, but they’re still pursuing Goldson, who said via his Twitter account that San Francisco still is in the running for his services.



Smith was drafted No. 7 overall and could replace Lawson in the lineup. He is one of several youngsters getting an extended look while San Francisco examines its options on defense.



“We’ve got a lot of jobs open, trust me,” said Vic Fangio, who took over as San Francisco’s defensive coordinator in January after Jim Harbaugh became the team’s new head coach.



“There are a few starting positions here that are solidified and most of the other ones are wide open. As it looks now, five starters from last year’s team at this moment are not here and don’t look promising for them to be here. So that’s a whole new defense right there when you have to replace at least half of them. It might be more.”



Smith’s position is a key spot in Fangio’s 3-4 system, which relies heavily on edge linebackers to apply consistent pressure on opposing quarterbacks.



That was Smith’s specialty at Missouri, where he recorded 17 sacks in 23 games over the past two seasons despite a broken leg that sidelined him for three games as a sophomore last year.



Smith rushed the passer from defensive end in college. The 49ers are moving the 21-year-old to edge linebacker in their scheme, and so far it has been a smooth transition.



“It’s been everything I expected and it’s been good so far,” Smith said. “Standing up and playing linebacker is an adjustment, but every day I play I’m getting more comfortable with it. It’s coming together now and I’m getting used to it.”



The 49ers already are getting used to Smith’s tenacity as he roams the field with an explosive first step and 84-inch wingspan that helps him keep blockers away from his body.



“He’s very impressive,” inside linebacker Scott McKillop said. “I didn’t realize how athletic he is. I’m eager to see everything he can do.”



With Lawson out, Smith is working with Parys Haralson, Ahmad Brooks and Thaddeus Gibson in the primary rotation at outside linebacker.



Haralson has been the team’s regular starter on the right side since 2008, but Fangio said that job could be up for grabs this year. Fangio also said he’s considering flipping his outside linebackers to opposite sides as situations warrant during a game.



“Right now, our outside linebackers are playing left and right, but that can switch,” Fangio said. “We don’t know exactly how we are going to play our guys. It’s way to early for that, but there’s less unsettlement there than we (have) in other positions.”