Long completed 19 of 32 passes before leaving the game midway through the third quarter, but Coach Hayden Fry was especially pleased with Harmon, who displayed the elusiveness he showed before breaking his leg against Wisconsin last November.
Said Fry: "After his (Harmon's) second TD run, I got the team together on the sidelines and told them, 'Ronnie's back.' "
The Hawkeyes, who pushed their nonconference record to 3-0, open Big Ten play against Michigan State next week.
Iowa State fell to 2-1 against an Iowa defense ranked first in the nation. The Cyclones' only points came on Rick Frank's 52-yard field goal with 9:21 left in the game.
Junior walk-on Rob Houghtlin set an Iowa single-game record by kicking for 14 points. He connected on 5 of 6 extra-point attempts and 3 of 4 field goals from 47, 41 and 27 yards.
Scott Helverson, who scored on pass plays of 46 and 25 yards, finished with 8 catches for 153 yards. Harmon, who also caught 6 passes for 56 yards, scored touchdowns on runs of 2 and 23 yards.
Iowa led, 7-0, after the first quarter, but Iowa State committed four turnovers in the second quarter as the Hawkeyes took a 41-0 halftime lead.
The Cyclones moved as close as Iowa's eight-yard line on their opening series, but the drive stalled when linebacker Larry Station chased down tailback Al Watson in the backfield and Frank missed a 26-yard field goal.
In addition to his 46-yard pass to Helverson, Long's touchdowns were 3 yards to Mike Flagg and 9 yards to Robert Smith. Iowa's first score came on a four-yard run by fullback Fred Bush.
Iowa has outscored its opponents 163-23 so far, and Long has completed 58 of 91 passes for 741 yards and 10 touchdowns.
Northwestern 38, N. Illinois 16--At Evanston, Ill., Mike Greenfield threw for a school-record 446 yards and fullback Casey Cummings rushed for two touchdowns as Northwestern won its second straight game for the first time since 1975.
Stanley Davenport rushed for a career-high 131 yards as the Wildcats raised their record to 2-1. It was the third straight loss for Northern Illinois (1-3) under first-year Coach Jerry Pettibone.
Greenfield, who played most of the game with a sore right shoulder that was injured in the second quarter, completed 19 of 31 passes for 367 yards in the first half.
That was five yards short of the NCAA record held by former BYU quarterback Jim McMahon, who threw for 372 yards in one half against Texas El Paso in 1980.
Greenfield finished 26 of 43 in passing for 1 touchdown with 2 interceptions.
Indiana 36, Missouri 17--Steve Bradley, Indiana's all-time total offense leader, threw for three touchdowns and rushed for another as the Hoosiers upset the Tigers at Columbia, Mo.
Bradley, a senior, completed 19 of 30 attempts for 265 yards and threw 1 interception. Sophomore Kenny Allen caught 10 passes for 183 yards, including a 64-yard bomb, for the most yardage a receiver has compiled in a game against Missouri.
The Hoosiers also rushed for 268 yards against the Tigers, who entered the game as a two-touchdown favorite.
The victory kept Indiana unbeaten at 3-0 while Missouri, under new Coach Woody Widenhofer, fell to 0-3.
Michigan State 7, Western Michigan 3--Lorenzo White's one-yard touchdown run with 3:07 remaining gave the heavily favored Spartans a comeback victory at East Lansing, Mich.
White's touchdown plunge capped an 11-play, 80-yard drive in which he carried the ball 7 times for 45 yards. For the game, White had 145 yards in 28 carries and tied a school record set by Eric Allen in 1971 with his fifth straight 100-plus effort. The nonconference victory gave Michigan State a 2-1 record entering Big Ten play next Saturday. Western Michigan fell to 0-3.
Wisconsin 41, Wyoming 17--Larry Emery ran for 136 yards and 3 touchdowns at Laramie, Wyo., as the Badgers (3-0) overpowered the Cowboys (1-3).
Emery ran one yard for a touchdown in the first quarter. He scored again on a one-yard run midway through the second period and added another touchdown on an eight-yard run in the third quarter.
Wisconsin's other scores came on a 22-yard run by Joe Armentrout, field goals of 37 and 25 yards by Todd Gregoire, and a 38-yard pass from Bud Keyes to Tim Fullington.