They said it was a temperature inversion, whatever that is, that caused an unsightly covering of smog over this pleasant city the other day. As seen by a visitor from his airplane window, the stuff was the color of water plunging out of rusty pipes: A dull orange. That was nice. Everything else in town is orange, why not the sky?

The Denver Broncos are an 18-year-old football team that is in the Super Bowl tournament for the first time. Like any 18-year-old who has found true, true love, Denver has gone slightly whacko. It hears music when there's no one playing. Its heart goes pitter-pitter-pat at the sight of a Bronco darling in his cute shoulder pads. And the color orange, the symbol of this bliss, is everywhere.

The football team's colors are orange and blue. The team's defensive unit is exceptional. There is a soft drink named Orange Crush. Naturally, then, the Broncos have come to be known as the Orange Crush. And the fevered imagination of moon-struck lovers has found a way to work orange into every nook, cranny and pocketbook this side of John Denver's guitar.

The Broncos, statisticians say, have enriched the area's economy by some $35 million this season by winning enough games to get into Sunday's American Football Conference championship game with the Oakland Raiders. The statisticians don't say how much of that loot went for orange pancakes, but some of it did.

We know that because a girl at a local McDonald's told us so. Right in front of her, she said breathlessly, there was Floyd Little, the former Bronco running back, eating orange pancakes. The newspapers and television shows here are delightful in their coverage of young love, sweet love. A tattoo artist called The Denver Post. He'd just etched a Bronco helmet on a man's bicep. A trucker painted his cab orange with white silhouettes of Bucko the Bronco, the team mascot.

"This town has gone crazy," said Ray Brennan, who like all taxi drivers is a sociologist at heart.

"Broncomania," Brennan said. He pronounced the word with respect. It was as if Horowitz spoke of his piano. "Driving a taxi, you get all kinds in that back seat.You get bad vibes. It can be bad. But talk about the Broncos and" - here Brennan smiled in wonder at man's humanity - "then everything is cool."

And here we are at Sweetwater's, a nightclub that gained a measure of notoriety this season by raffling off chances to throw a brick at Howard Cosell's image every Monday night. A rock group is playing, girls are dancing, the beer is cold. Journalism is hell. And here comes a guy in an orange T-shirt.

"Are you a Bronco fan?" he asked.

Discretion being the better part of valor, the Ann-Margret fan said, "Yes, sir."

"Look here, this is what we're going to do to Stabler."

The man had one of those iron-on emblems that decorate tee-shirts nowadays. This one had a big, orange D with Bucko the Bronco stomping on a black-clad Ken Stabler, the Oakland quarterback. "CRUSHED AGAIN," the emblem said, and the man twirled around, displaying the tee-shirt.

"How much?" the Ann-Margret fan said.

"Four bucks," the tee-shirt man said.

An expense account will absorb only so much foolishness, so that tee-shirt man was sent away. It was an act of will apparently beyond the capabilities of most consumers here. A beauty salon operator said she has dyed several heads of hair orange. A man spent $16,000 customizing a van that is orange with football-shaped windows. For Christmas - or Crushmas, as it was called here - they sold orange Christmas trees.

When a building was to be knocked down this week, someone put an Oakland Raiders banner on the front wall. From a cable on a crane swung the demolition ball. Painted orange. Cheers all around when the orange ball smashed the banner and incidentally, the building, to smithereens.

From all this orange it's difficult to squeeze a favorite. You can buy an Orange Crush pizza the ever popular ham-and-shredded carrot model. By blending Orange Crush with vodka, you create a screwraider. Telephones, TV sets, carnations and dog sweaters come in orange. To demonstrate that entrepreneurs will go to all ends, there's an orange hot seat cushion. "Hot Seats are 16 inches square and warm your backside by heat reflection," a half-page advertisement said.

Broncomania. Broncobliss. Love has many names in the Rockies today. The Raiders' coach, laughing bear named John Madden, walked into a hotel gift shop two nights ago. There was an Orange Crush tee-shirt for sale. "Wonder if they got one to fit me," he said. It was a joke. He isn't Bronconuts.

Has Denver gone ape?" "More like Orange-utans!" The Denver Post said in a headline. The Rocky Mountain News, checking all angles, asked local ministers if they planned to change the times of Sunday services so worshippers can see the Bronco game beginning at noon.

"We'll have a huge 9:30 a.m. throng and a very quiet 11 a.m. service," said the Rev. William G. Cooper of Phillips United Methodist Church. The second service will be long, he said, "only if I want to die young."