Defensive coordinator Monte Kiffin, the mastermind behind the dominating unit of the Tampa Bay Bucs, has agreed to a new contract that will make him the NFL's highest paid assistant coach and keep him with the Super Bowl champions, ESPN.com has learned.

The deal, negotiated by agent Jimmy Sexton, was reached Thursday afternoon, shortly before Kiffin was to have boarded a flight to the West Coast to interview for the San Francisco 49ers head coaching position. League sources agreed Kiffin would almost certainly have been the frontrunner for the Niners' job had he made the trip.

The contract is for three years and, with a value of $5.1 million, sets a new standard for assistant coaches. It includes a $1.1 million signing bonus and base salaries of $1.2 million (2003), $1.3 million (2004) and $1.5 million (2005). By comparison, Philadelphia defensive coordinator Jim Johnson last week signed a four-year contract worth $3.6 million, a deal believed to be the richest for a league assistant.

In terms of the annual average, $1.7 million, the new Kiffin contract nearly doubles that.

Between the signing bonus and base salary, Kiffin will earn more in 2003 than nearly one-third of the NFL's head coaches. The average for the deal is also more than the mean for several head coaches.

Early in the 2002 season, Kiffin had signed a two-year extension through 2004, a deal worth about $1 million annually. The contract agreed to on Thursday supercedes that one.

The agreement culminated 24 hours of hectic negotiations between Sexton and Bucs vice president Joel Glazer. The two spoke well into the night Wednesday and then resumed discussions Thursday.

On Wednesday night, Kiffin spoke by phone with 49ers general manager Terry Donahue, who hopes to have a successor to Steve Mariucci in place by no later than next week. It is not known how the withdrawal of Kiffin as a candidate will affect the 49ers' search for a head coach.

Bucs coach Jon Gruden, within minutes of his team's Super Bowl XXXVII victory Sunday night, announced the franchise would do everything it could to retain Kiffin. That was before San Francisco officials had even contacted the Bucs for permission to speak to their coordinator.

Kiffin, 62, for years has been one of the premier defensive minds in the NFL, but finally received his public due only in the last two years. Obviously, the Super Bowl victory, in which Tampa Bay thoroughly throttled an Oakland offense that was statistically ranked No. 1 in the league, further elevated his profile and his reputation.

The Bucs have ranked among the NFL's top six defenses in each of the past six seasons and were rated No. 1 in 2002.

Len Pasquarelli is a senior writer for ESPN.com.