PRESIDENT CARTER and former California governor Ronald Reagan have joined the Pittsburgh Steelers as the betting favorites in their respective contests. For the Steelers, it will be Super Bowl XIV in Pasadena today. For the president and Mr. Reagan, it will be the Iowa caucuses tomorrow. But there is a very significant difference between the contests and especially in the way the opponents, the non-favorites, are approaching the encounters.

Ray Malavasi is the head coach of Pittsburgh's opponent, the Los Angeles Rams. While most head coaches would like very much to bring their team to the Super Bowl, the trip loses a little of its appeal when it means playing Pittsburgh once you get there. If Gen. George Patton's Third Army had been a football team, it would have been the Pittsburgh Steelers. But nobody has yet recorded Ray Malavasi saying anything like "if we show up for the second half, it will really be a victory for us, regardless of the score."

Unfortunately, the Malavasi brand of primitive logic does not apply to presidential candidates. We are learning from the almost hourly dispatches out of Des Moines and Davenport that Sen. Howard Baker will be a "winner" in the Iowa caucuses if he finishes a "respectable third." Sen. Edward Kennedy's campaign spokesmen had stated that President Carter, in order to claim an Iowa victory, must match the 57-to-25 margin he held over Sen. Kennedy in the most recent Iowa public opinion poll. Gov. Edmund Brown Jr. has cutely sidestepped a probably Iowa defeat by entering into an unsolicited coalition with the firstplace finisher in the 1976 Iowa Democratic caucuses: Uncommitted. Some non-Reagan Republicans are arguing that Mr. Reagan must equal or better the 48 percent he got in 1976 in a two-man contest with Gerald Ford (conveniently ignoring the fact that Mr. Reagan has six opponents this year).

Las Vegas has been good enough to extablish a point spread in football for people who enjoy a game more when they have risked a bob or two on the margin of victory or defeat. Politics, a less scientific art than football, has been spared this wrinkle. In elections, somebody wins and more somebodies lose.. The somebody who wins is the one who receives more votes than any other somebody.

Iowa has not changed the date, time, place or form of its presidential caucuses. Every candidate who has entered the race has known that Iowa would be first and more important than Maryland or Massachusetts, because it is first. It is altogether too early in the year to start proclaiming or recognizing "moral victories." As for us, we are interested in who wins in Iowa tomorrow and in Pasadena today.