The Fighting Irish moved up from No. 3 to the No. 1 spot because it is now the last eligible undefeated team in the country. Notre Dame is the third new No. 1 team in the past three weeks.
"Now we don't have to answer questions about style points or politics," Notre Dame coach Brian Kelly said. "Now we have a chance to play for the national championship this week."
Notre Dame, ranked No. 1 in both polls and by the computer ratings, needs only to beat slumping rival Southern California on Saturday in Los Angeles to earn its first trip to the BCS title game.
Oregon fell to No. 5 after its first loss of the season, and Kansas State paid the price for getting blown out, dropping five spots to No. 6.
Florida is ranked second in five of the six computers despite being fifth in the Harris poll and sixth in the USA Today poll. Oregon's computer average is seventh, and Kansas State's is fourth.
No. 7 LSU is the highest ranked two-loss team.
Stanford jumped five spots to No. 8 after upsetting the Ducks.
No. 9 Texas A&M is the fifth SEC team in the top 10.
The ACC gets no respect in the computers -- the Seminoles' average is only 17th, and Clemson's in 15th.
Like Notre Dame, Alabama and Georgia also have rivalry games Saturday. The Crimson Tide host Auburn and the Bulldogs play Georgia Tech at home.
If the favorites win, the SEC championship game will be a national semifinal of sorts, with the winner advancing to the BCS title game.
Notre Dame, which last won a national championship in 1988, has lost nine of the last 10 against USC, the lone victory coming in 2010, Kelly's first season as coach.
But the Trojans have been a major disappointment this season, starting at No. 1 and dropping to 7-4 after losing Saturday to UCLA. They also will be without quarterback Matt Barkley, who sprained his shoulder at the end of Saturday's UCLA matchup and was deemed out for the Irish game by coach Lane Kiffin on Sunday.
If Notre Dame loses, it could leave a muddle of one-loss teams vying for a spot in the BCS title game, even opening up the possibility of a second consecutive all-SEC national championship game.
Information from The Associated Press was used in this report.