Pittsburgh is a seven-point favorite over Houston for the AFC championship Sunday in Three Rivers Stadium. Dallas rules a 3 1/2-point choice over Los Angeles for the NFC title later the same afternoon in the Coliseum. The winners will go to Super Bowl 13 where, if form holds, the Cowboys will be a four-point pick over the Steelers.

The Steelers should get to Miami for the Jan. 21 classic. They were by far the most impressive of the four victorious teams last weekend, dismantling a strong Denver defense in impressive fashion.Dalls and Los Angeles and to struggle before disposing of Atlanta and Minnesota. Houston caught a New England squad that was afraid to put the ball in the air with its first-string quarterback.

Pittsburgh appears to have by far the best balance of the final four. Chuck Noll's offense probably is a shade better than his defense at this point, but both units are solid and they know how to take advantage of the home field. Never discount the importance of the home field when the Steelers are involved.

Houston is in a hot streak and luck has been on its side. The ball keeps bouncing in the Oilers' direction. There is no way, however, that Houston's defense can shut down both Terry Bradshaw's passing and Franco Harris' running. The Steelers will score at least 20 points unless bad weather intervenes.

Earl Campbell must produce another tremendous afternoon if Houston is to stay close. The rookie is capable of doing just that. And Dan Pastorini continues to perform surprisingly well, but he is a relatively stationary target and his string of unexpected successes should end right about here.

Why is it, by the way, that Pastorini seems to be throwing better in his "straightjacket" than he did when he was healthy?

I will invest an imaginary $250 on the Steelers. Had the number for the game been less than seven, I would have increased the play accordingly.

Los Amgeles attracts an imaginary $100. The Rams have everything in their favor except for Coach Ray MaIavasi's lack of imagination.

Too Tall Jones in carrying the Dallas defense on his superstructure. He has to, since Harvey Martin has been unable to overcome injury problems. Randy White, meanwhile, continues to be one of the most trapped tackles in the NFL.

The Rams' major concern is their quarterback, Pat Haden. If the Rhodes scholar can keep from making costly mistakes, the L.A. defense has a splendid opportunity to carry the day. Ron Jessie completely baffled cornerback Binnie Barnes in their first meeting this year and he could do it again. The left wing of the Dallas secondary is very vulnerable.

But how could anyone become too serious about backing the Rams at this stage of their career? This is a club that, time after time, has manage to produce a defeat from an imminent victory, and they are eminently capable of doing so again.

Dallas certainly will be the more resourceful team on the field. But the mathematics dictates the pick, and Los Angeles, getting 3 1/2 points, has a safety cushion attached. A final score showing Dallas winning by 3 points is quite likely.

This column was for four in the playoffs last weekend, covering the spread with Pittsburgh andLos Angeles but failing with Dallas and New England. One can root just so long and so hard for the home team these days.

This kept the ledger for the season at one game under.500, at 33-34. More important, the net result was a loss of $200 of the imaginary bankroll, reducing the total profit from $515 to $315.