How good is the Pittsburgh vs. Dallas showdown Sunday? Better than anything known so far as the Super Bowl. None of the 12 previous roman-numeral festivals have had two teams so talented and mature. To find anything comparable, one must recall those ancient times when the game simply was known by what it is: the National Football League championship.

Lombardi's Packers of Super Bowls 1 and 2 and Shula's Dolphins of Super Bowls 7 and 8 were the equal of the Steelers and Cowboys. But they never played each other. And Sunday's game should be attractive, oddly enough, because neither team has an obviously exploitable weakness.

"If you prepare to go at some area or somebody," said Dallas offensive tackle Pat Donovan, "your attack is slightly imbalanced. And if the defense stops that, you've got to resort to tricks or things you've not really worked on that much."

Both teams have players and units stronger than others. But no weaknesses such as the uncomplicated Colt zone Joe Namath tore apart or the clearly vulnerable Viking front four or the Redskin mental droop four days before the kickoff.

The major reason the Steelers are slight favorites is Terry Bradshaw. If he has a good to excellent game, Pittsburgh should win its third Super Bowl. Anything less and the Cowboys gather in their third success.

Other reasons, for and against both teams, are a bit more complex -- and the best way to judge them is not the traditional player against player but unit against unit. So...

PITTSBURGH OFFENSE VS. DALLAS DEFENSE

Up front, it's the left-handed Steelers vs. the right-handed Cowboys. Pittsburgh likes to run to its left, as would anyone with Jon Kolb at tackle, Sam Davis at guard and, best of all, Mike Webster at center. Franco Harris and Rocky Bleier will be headed toward the Cowboy strength, Harvey Martin and Randy White.

With Martin, White and Too Tall Jones, Dallas would seem to have the advantage on pass-rush situations. But the Steelers usually keep Harris or Bleier in to block anyway. The wide receivers, Lynn Swann and John Stallworth, caught nearly 50 percent of the Steelers' passes this season.

The Dallas cornerbacks, Benny Barnes and Aaron Kyle, are said to be ordinary, the safeties, Cliff Harris and Charlie Waters, excellent. The one Cowboy one-on-one advantage should be strong-side linebacker Thomas Henderson against tight end Randy Grossman.

Like Dallas quarterback Roger Staubach, Bradshaw is a running threat and excellent on improvised passes. He has realized the enormous potential he brought into the NFL nine years ago.

The Pittsburgh offense actually relies more on finesse, traps and the like, than on power. The Dallas defense is designed to stop runners like Harris. The advantage goes to Pittsburgh.

DALLAS OFFENSE VS. PITTSBURGH DEFENSE

The Cowboys do not have a hall-offame offensive line, but Tony Dorsett often makes it appear this good. Pittsburgh's front four is not as good as when the teams met in the Super Bowl three years ago, but the linebackers are better.

Dallas' offense is more versatile than Pittsburgh's, with five players having caught at least 34 passes each. And the vastly underrated Robert Newhouse returns at fullback, although the finger injury to third-down receiver Preston Pearson could be more troublesome than the Cowboys let on.

Staubach has not been especially sharp in the playoffs, but had a slightly better regular season statistically than Bradshaw. His offense is superior to the '75 unit that mustered 17 points against the Steelers (to Pittsburgh's 21) because of the speed of Dorsett and wide receiver Tony Hill.

"No flip-flopping (their linebackers) when the tight end shifts will make it easier for the Steelers to adjust to the various formations Dallas will show them," said the Miami Dolphins' director of pro scouting, George Young.

Of the front four, Young said, "L. C. Greenwood and Joe Greene are getting up there in years (both at 32). But this still is a formidable group. A lot of times, people try to run at Greenwood, but he's so well protected with Jack Ham on one side and Greene on the other."

Pittsburgh has allowed opponents only nine points in the first quarter of 18 games. And Dallas is better leaping out on top than coming from behind. The advantage is miniscule, but goes to Dallas.

One conclusion seems clear: even though both teams have terrific defenses, the game should be relatively high scoring.This is because both coaches, Chuck Noll of the Steelers and Tom Landry of the Cowboys, have shed the can't-win-the-big-one label and will allow the teams to play boldly.

Both teams are capable of scoring three touchdowns each. But the one Steeler weakness -- and it could be a big one if the Cowboys get ahead early -- is placekicker Roy Gerela. He was erratic most of the regular season, but four-for-four from inside 40 yards during the playoffs.

His Dallas counterpart, Rafael Septien, made 16 of 26 field-goal tries during the regular season. Both punters are quite accurate, especially Pittsburgh's Craig Colquitt; neither has great distance.

The return men for both teams are good, but hardly in the Rich Upchurch-White Shoes Johnson class. For kicks, the advantage goes to the Cowboys.