It took two decades to create "Oriole Magic" here.

It took two months to kill it.

Each night and day of the Orioles' current home stand, the same sad scene is played out in Memorial Stadium. As the Birds run onto the field, the public address system explodes with the incongruous song, "Oriole Magic, Feel It Happen."

Fans clamp their hands over their ears in pain, players look at the blaring mezzanine speakers quizzically and reporters in the press box complain.

And, at each game, an O's oficial says into his telephone, "Turn down the volumn on the PA. There aren't enough people int he park to absorb the sound."

The O's guess what "normal" attendance would be on such a night for such a foe. Then, based on the experience of past seasons, they set the decibel level.

At every game, the guess is far, far too high.

In baseball's second season, Baltimore attendance is down by a staggering 28 percent compared with the first half of this year. Only three teams in baseball -- Cleveland, Atlanta and San Diego -- have been bludgeoned worse.

More incredible, in their 15 home dates since the Aug. 10 resumption of the season, the O's have drawn an average crowd of only 16, 391. Just a year ago, in the first 15 Baltimore home dates after Aug. 10, average attendance during the heat of the pennant race was 33, 765.

By that perhaps slightly exaggerated measure of comparison, Oriole attendance has plummeted by more than 50 percent.

Baltimore owner Edward Bennett Williams could, if he wished, quibble that, after 38 dates, the Birds have actually drawn 34,887 more people than they did a year ago. But Williams has faced the truth. "I figure we're off by 30 percent," he said.

For 20 seasons, the Orioles played superb baseball. But Baltimore didn't particularly care. A top attendance year was 1 to 1.2 million fans.

Then, the last two years, Baltimore did better by the Birds with attendance of 1.7 and 1.8 million. In other words, Blatimore, at maximum fever pitch, managed to reach the major-league median in attendance.

Now, the calendar has gone backwards. The mood at Memorial Stadium has reverted. Once again, the ballpark on 33rd Street is a sleepy enclave where connoisseurs discuss the subtleties of Bird ball without having their nerves jangled by too much excitement.

The current attendance is exactly what it used to be: about a 1.1-million pace. Perhaps the hard-core fans returned, but the cheap-thrill, in-thing-to-do folks have gone back to Dallas and disco.

When the Star-Spangled Banner's line, "Oh, say, can you see," is sung, what was once a shocking eruption for the "O" -- a noise so loud it sounded like a bomb explosion at the '79 World Series -- has now sunk to a half-hearted whisper.

Self-appointed cheerleader Wild Bill Hagy has gone on the baseball wagon for the rest of the season; he actually got his cowboy hat mangled in an upper-deck punchout last week.

But even Hagy, standing on the dugout spelling "O-r-i-o-l-e-s," or at least something fairly close to it, with his body, is already missed.

Even the homiletic Bird broadcasters, who contribute to the team's hick national image, have adopted a tone of alienation from the sport that would seem more at home with New York nasalisms that a Bal'mer drawl. Even Chuck Thompson can't bring himself to say, 'round about the eighth inning, how many wonderful seats are still available.

"Ou don't realize how important the people are to the game until they're gone," said Baltimore General Manager Hank Peters.

In Baltimore, they're definitely gone.

And nobody knows if they're coming back.

Standing in his owner's box Friday night, Williams looked out over a crowd of 15,733 for an Oakland game that, a year ago, might have drawn twice that many. "I feel like a farmer waiting for rain," he said.

"Hang in there," commiserated Nestor Chylak, an AL umpire supervisor. "The fans'll come back."

"I hope so," said Williams. "My fingers are getting tired from hanging on to the edge of this cliff."

Plenty of factors are working against farmer Williams and his crop.

The ludicrous split season has hurt. "Fans don't regard a 13-10 record as meaningful," said Williams. "It's a dull, early-May kind of record."

If a continuous season were still a fact, the Yankees would now be in first place by half a game over detroit, with both Baltimore and Milwaukee jus 1 1/2 games out. "But now," said Coach Ray Miller, "they post the Yankees' score and, instead of a roar, it's a yawn."

"Our hope," said Peters, "is that people will realize how little of the season is left. On Sunday, half of our second season will be over."

Also undermining the cause is the Birds' own play. "We have not been playing well at all," said Williams. "We haven't looked good winning and we've looked awful losing -- narrow victories and horrible defeats."

Every aspect of the split season seems ill-suited to Oriole tastes and talents. The Bird brass refused to hype the second opening day one iota, preferring to bite the bullet rather than perpetrate the fraud of trying to make a buck off the strike. Even the honesty of Williams and Peters throughout this season has probably cost them money, since they have refused to say the sport was wearing a fine new suit of clothes when, in fact, it was naked.

The Orioles were built to thrive on an arduous, 162-game season in which depth of pitching, fundamentals, defense, steady professional effort and Manager Earl Weaver's percentages grind down less complete and craftsmanlike teams. This season, however, is made for a fluke team playing on adrenaline, streaky offense, suspect pitching and the novelty of being alive in September. Read, the Detroit Tigers.

The Orioles seem to know this. They will have to resist the strong impulse, felt by many of their fans, to give a Garry Templeton salute to the rest of this season, then start fresh on significant business in '82.

In a sense, being a champion in '81 is a prize hardly worth winning. Certainly, the Orioles, hitting .201 in this home stand, are playing that way. Their magic has gone the way of their crowds.

"It's been proven that the more people in the prk, the better the home team plays. The crowd affects the tempo and enthusiasm of the game," said Peters. "Unconsciously, maybe we don't have quite the get up and go we did before."

Friday, a priest led a prayer before the game.

"I believe the monsignor is praying against pornography," muttered Williams. Then, leaning forward, the owner rasped, "Pray for hits, man. Pray for hits."

Or, he might have added, fans.