PITTSBURGH - James Harrison isn’t one of the NFL’s biggest bargains any longer.

The Pittsburgh Steelers outside linebacker reached terms Monday on a $51.75 million, six-year contract that will make him the second highest-paid player in franchise history.

The contract set to be announced Tuesday will pay the NFL Defensive Player of the Year a guaranteed $20 million — more than any other player in team history except Ben Roethlisberger. The quarterback signed a $102 million, eight-year contract last year that will pay him a guaranteed $36 million.

Harrison broke into the Steelers lineup in 2007 and had 8½ sacks. He had a Steelers-record 16 sacks in 15 games last season, and his 100-yard interception return for a TD — the longest scoring play in Super Bowl history — helped the Steelers beat Arizona 27-23 for their second NFL championship in four seasons.

Harrison, cut four times earlier in his career, cashed in after being an NFL starter only two seasons. The 30-year-old Harrison was about to enter the final season of a $5.5 million, four-year contract he signed as a backup in 2006. He would have made $1.4 million this season.

“James is pleased he will be a Steelers for the rest of his NFL career, in all probability, which is what he wanted,” said Bill Parise, Harrison’s agent. “The contract is reflective of him being the defensive player of the year.”

According to Parise, the contract is the largest signed by an NFL linebacker, although Harrison is not guaranteed of being paid the total value of the contract.

The Steelers made re-signing Harrison a priority — and, in a coincidence, his guaranteed money is about that Porter is getting after signing with Miami following the 2006 season. With Harrison ready to play, the Steelers felt they could not pay that kind of money to Porter, even after he helped them win the Super Bowl during the 2005 season.

Harrison and the Steelers began talking about a new contract not long after the Super Bowl was played and the deal was concluded before the Steelers officially begin their offseason workouts next week, although many players already are working out at their practice complex.

Harrison is the only undrafted player to win the Defensive Player of the Year award. He played at Kent State, the alma mater of former Steelers All-Pro linebacker Jack Lambert, but was cut by the Steelers and Ravens and spent one spring playing in NFL Europe before finally landing a job with Pittsburgh in 2005.

Slideshow   The Week in Sports Pictures The Giants on top of the football world, getting ready for the London Olympics and more. more photos

Harrison turns 31 next month, so it is unlikely he will play for the entire length of a contract that runs through the 2014 season.

The Steelers also have re-signed backup linebackers Andre Frazier, Keyaron Fox and Arnold Harrison since the season ended. They have not signed any major free agents from other teams, but have reached new deals with Harrison and left guard Chris Kemoeatu, who will make $20 million over five seasons. Like Harrison, Kemoeatu moved into the Steelers’ lineup after an All-Pro player — Alan Faneca, now of the Jets — signed with another team.