OVERWORKED?

When he turned 25 last September, Clinton Portis was the Washington Redskins’ franchise player, had more than 1,200 carries and was owner of the richest running back contract in NFL history.

Portis was an anomaly, a runner who produced early, got traded early and got paid early.

But the bill might be coming due.

As he prepares to start his sixth NFL season Sunday when the Washington Redskins play host to Miami, Portis is facing more questions than at any point in his pro career.

Will his knee, which caused him to miss all of the preseason, hold up for 16 games?

Will his surgically repaired left shoulder stay in one piece given his upright running style?

Can he regain the form he showed in 2005, when his five straight 100-yard games propelled the Redskins to the playoffs?

“If we don’t win this year, it could be it for a lot of people,” Portis said yesterday. “If I don’t do what I’m supposed to do, a lot of things will be changing.”

Portis admitted last week that one of those changes could be him and his bloated contract, a $50.5 million deal signed in March 2004 upon his trade from the Denver Broncos.

Teammates who have seen him in practice the last week think it’s possible for Portis to return to full strength sooner rather than never.

“I think it’s realistic,” running back Rock Cartwright said. “He’s fresh, he’s healthy and he’s practicing at a high level. He’ll get in there and do his thing. … His intensity has picked up, and he’s cutting like he used to.”

Said fullback Mike Sellers: “The dude’s in shape. … Everybody’s second-guessing him because of his injury. I don’t second-guess him at all.”

It’s unclear how much work Portis will get against the Dolphins, his first game since Nov. 12. He made it through only four days of training camp this summer before being shut down for a month. It is expected Portis will start, but Ladell Betts will get more carries.

Portis went through his fourth consecutive practice yesterday at Redskin Park and reported no pain in his right knee, which developed tendinitis in mid May.

“I feel like I’ve done everything possible to get ready,” he said. “I think I can handle any workload given to me. I’m not going to pout and ask for more and complain and say I needed less. Whenever my number is called, I’ll respond.”

Considering his epic workload from 2002 to 2005, it’s a wonder Portis still can be effective.

Before he turned 25, he had seasons of 273, 290, 343 and 352 carries. The 1,258 attempts and 5,970 yards are more than any other current starting running back had before the age of 25.

The only other two backs to carry a similar load are Edgerrin James (1,184 attempts), LaDainian Tomlinson (1,024) and Jamal Lewis (1,004).

While Tomlinson continues to be an athletic freak, Lewis and James are feeling the effects of doing so much so soon. Lewis, now 28, was allowed to walk when Baltimore traded for Willis McGahee. He signed a one-year deal with Cleveland. James got his money by signing with Arizona before last year but then experienced his worst full season as a pro.

By comparison, Larry Johnson (140 carries before age 25), Deuce McAllister (692), Shaun Alexander (373) and Brian Westbrook (163) were backups when they first entered the league and/or spent four to five years in college.

Asked whether he wished his workload would have been lightened early in his career, Portis said: “In college, I shared the load. … With Denver, I shared the load. I got here, and they wanted me to be the focal point.”

Portis accounted for 56.3 percent of Denver’s carries in 2002-03. That figure jumped to 72.8 percent with the Redskins in 2004 and 67 percent in 2005.

Associate head coach-offense Al Saunders is in favor of one workhorse back, and Johnson and Priest Holmes had monster seasons for him in Kansas City. But Portis is different. He will pull himself out of the game when winded with Gibbs’ blessing. On Sunday, Saunders will have no choice but to use two backs and listen to Portis as to how much he can handle.

“He has to let us know,” Saunders said. “We’re not inside his body, so we have to trust his judgment in terms of what kind of load he’s capable of taking. We all know Clinton has great ability. The important thing is that he has the energy that he’s used to playing with. He’ll only know when he gets in a game.”

And the Redskins will know what they have in Portis only when he gets in a game.

“I’m waiting to see just like you are,” cornerback Shawn Springs said. “I know Clinton’s a competitor, and I know he’s worked really hard. … He knows his importance to our team. He knows what we expect. We need him to perform.”