1981 college football season is a tough one to explain

At some point this season six teams have been ranked No. 1, and possibly none of them will appear in a major bowl - Rose, Sugar, Orange, or Cotton. Just how could this almost unimaginable situation come to pass? To find out, let's run down the present status of each school.

Michigan, which started off the season No. 1, would be shut out of the Rose Bowl if it loses to Ohio State this Saturday. Iowa would then go, unless it loses to Michigan State, in which case the Buckeyes represent the Big Ten Conference.

Notre Dame saw the bottom fall out after losing to Michigan and now owns a very unimpressive 5-4 record. With games upcoming against Penn State and Miami of Florida, Coach Gerry Faust's top priority is to avoid a losing season, not think about bowl appearances.

Southern California has a shot at going to the Rose Bowl, but the complicated Pac-10 race leaves little hope of that. The Trojans would have to beat UCLA Saturday while Washington and Washington State tie. Washington State goes if it wins; Washington gets the nod if it wins and USC beats UCLA; and UCLA goes if it wins and Washington beats or ties Washington State.

Texas appears to have the inside track on hosting the Cotton Bowl, but the Southwest Conference race has about as many permutations as the Pac-10's. Arkansas is still in contention and would grab the Cotton berth if Texas loses either one of its last two games against Baylor and Texas A & M and Arkansas beats Southern Methodist this weekend. (SMU is bidding for its first league title since 1966, but is on NCAA probation and banned from post-season play.)

Penn State was thought to be a serious contender for the national championship until dropping back-to-back games to Miami and Alabama. The Nittany Lions have slipped from first to 14th in the UPI poll as a consequence.

Pittsburgh should still be undefeated when the bowl bids go out Saturday night, right after meeting Temple and a week before playing Penn State. With a perfect record Pitt will pretty much have the pick of postseason destinations.

The Panthers could wind up in the Sugar Bowl playing the Southeastern Conference's representative, either No. 3 Georgia or No. 4 Alabama. On the other hand, if they elect to seek out the highest-ranked opponent available, that would be No. 2 Clemson at this point.The only way to achieve this matchup, however, is for both teams to choose a bowl beholden to no one, say the Fiesta in Tempe, Ariz. The ''big four'' bowl games all have conference tie-ins, yet the Fiesta, which is switching from Dec. 26 to New Year's Day, could pair Pitt, an independent, with Clemson of the nonaligned Atlantic Coast Conference.

Even if all these ''ifs'' should come to pass, Michigan and Southern Cal might wind up playing in some other major bowl besides the Rose. Both are name teams, and what bowl wouldn't love to hype the appearance of USC tailback Marcus Allen or Michigan receiver Anthony Carter?

But there's no guarantee this would happen, since losses Saturday could drop these giants behind two other teams in their respective conferences. Yale loss shocks Ivies

Everything was supposed to be so clear-cut this year. Yale would win the Ivy League title with ease, fielding one of those rare Ivy powerhouses that merits Top 20 consideration.

Thus it was that undefeated, untied Yale swaggered into last Saturday's game with Princeton, which hadn't beaten the Elis in 14 years. What had the makings of a tuneup for the Harvard-Yale game looked to be just that as Yale jumped out to a 21-0 lead. Princeton fought back, though, and ultimately won 35-31 on Bob Holly's bootleg with four seconds left.

For Princeton rooters, this was even better than Harvard's famous 29-29 ''victory'' over another undefeated Yale squad in 1968. Harvard scored 16 points in the last 42 seconds of that game, stalling a Yale juggernaut led by Calvin Hill and Brian Dowling. Yale has another superb backfield tandem in tailback Rich Diana and QB John Rogan. Diana gained 222 yards against Princeton , yet the day belonged to Holly, who set an Ivy passing record with 501 yards.

Now Yale could see the Ivy crown slip away to Dartmouth, or possibly even Harvard or Princeton, in the final week of the season, depending on Saturday's results. Scheduling pitfall in the South

A glaring shortcoming in the Southeastern Conference schedule has made for a very sticky problem. Georgia and Alabama will probably wind up with identical 6 -0 conference records, but because they don't play each other, who's to say which team deserves the league's automatic Sugar Bowl berth? Georgia has actually already completed its conference slate, but Alabama must still play Auburn on Nov. 28.

Reports have circulated that the Sugar Bowl selection committee will invite Georgia to play Pittsburgh, though no official announcement can be made until Saturday night. This matchup would provide more than a little deja vu since both teams have claimed national championships playing in New Orleans. Georgia did so last January by beating Notre Dame in the Sugar Bowl, while Pitt locked up the No. 1 rating in 1976 by defeating Georgia. Of course, Alabama claims the same distinction, using Sugar Bowl victories after the 1978 and '79 seasons to secure the top rankings.

Incredibly, the Southeastern Conference's revolving schedule hasn't seen Alabama and Georgia play since 1977 and won't pair them again until 1984. So maybe the Sugar Bowl should do the league a favor and bring both teams to New Orleans for an all-SEC showdown. Big Eight rivals Nebraska and Oklahoma went at each other in the Orange Bowl three years ago after meeting in the regular season, so such an in-house bowl game is certainly not unprecedented. And this one would have the advantage of not being a rerun.