A HOLE IN THE GROUND, A HOLE IN THE HEAD . . .

Geraldo Rivera recently was named a semifinalist to be the first journalist in space. Too late. As he showed Monday night, he’s already in space.

We should have suspected the worst when the former “20/20” star and exponent of “wow” and hero journalism showed up wearing dramatic black, sort of like Zorro.

Rivera--who writes in the current Esquire magazine that he was unhappy because the ABC “news establishment (was) intent on keeping me out of Credibility Hall”--was absolutely giddy during Monday night’s two-hour telecast of the opening of mobster Al Capone’s so-called secret vault in Chicago.

As we now all know, the vault (there seems to be only one) contains Prohibition era--ta da!--dirt.

With Geraldo in town, though, the Windy City was never windier.

Titled “The Mystery of Al Capone’s Vaults,” the live program should have been called “The Mystery of Geraldo Rivera’s Schmaltz.”

Equally mysterious is why so many Americans got suckered by this sprawling, spewing, ersatz event that Tribune Entertainment syndicated abroad and to a whopping 181 stations in the United States, including KTLA Channel 5. Everyone profited from this non-event except viewers who tuned in expecting something.

Overnight Nielsen ratings showed “The Mystery of Al Capone’s Vaults” bagging 61% of the viewers in Los Angeles, 73% in Chicago, 61% in Denver, 53% in Detroit and 45% in New York. Officials at Channel 5 here said it grabbed the biggest audience in the station’s history--nearly 2 million homes--and was the sixth-highest rated single show in Los Angeles TV history.

Rivera did more than merely host the program. He massaged it. He honked it. He oiled it. He greased it. He oozed it. He huffed it and puffed it. He overstated, overrated and inflated it. It was a tight call as to what was more abundant, the bull, the commercials or Geraldo’s wardrobe changes.

Interest had been building for months (we were told) about the concrete vault beneath Chicago’s long-abandoned Lexington Hotel, once the notorious Capone’s headquarters. The massive bunker was said to have been built by Capone in the 1920s.

What would be inside? Skeletons? Capone’s millions? The Marcos billions? Imelda’s garter belts? Dr. Ruth? Geraldo’s credibility? Hardly.

As viewers were to discover, there were two empty vaults in Chicago Monday night. One was in the basement of the Lexington Hotel, the other inside Rivera’s head.

“I’m Geraldo Rivera and you’re about to witness a live television event,” he gasped. “Now, for the first time, that vault is about to be opened live.” He added: “This is an adventure you and I will take together.” He went on: “One way or another, this mystery is going to be resolved.”

At this point, my 17-year-old daughter turned to me and asked: “This is a half-hour show, huh?” I told her it was two hours.

“Are you serious?” she replied. “No way.”

With Geraldo, there is always a way. “The mystery is being solved,” he announced, a man in action. “All right, let’s get going.” He breathlessly described Capone. “His attraction to physical violence.” Ooooooooh! “His ability to commit cold-blooded . . . murder.” Grrrrrrrr!

With each explosive charge, with each commercial, Geraldo grew more excited, sometimes almost babbling.

The music and host swelled simultaneously. Rivera (who complains in Esquire that he was “the outsider at ABC, the passionate oddball barely tolerated, almost never acknowledged by the Prep School Mainstream”) was now directing the opening of Al Capone’s vault. Maybe it was Capone’s vault. It was somebody’s vault. Well, at the very least, it was a vault. Wasn’t it?

Forget the vault. First, it was time for a taped segment glorifying crime, time for Geraldo to don the protective goggles and learn how to use a Capone-era Thompson submachine gun.

Scarface Geraldo squeezed off a few bursts at a wall, examined his work and marveled at the weapon’s efficiency, then squeezed off a few more bursts. “This is live ammunition,” he crowed. “It’s not like the shows you see on TV.”

Oh, Geraldo. We knew if you did it, it had to be real.

Back live now to the vault. “OK, guys,” Rivera exhorted his blue-outfitted demolition crew. Then to everyone else: “Gotta clear the basement! Everybody out!”

But first, the program’s 1,400th commercial. Then back to Rivera, now wearing an orange hard hat as he warned: “Thirty seconds!” Then, kneeling over a Capone-era dynamite plunger, the man who couldn’t get “no respect” from ABC News began his dramatic countdown. “Five . . . four . . . three . . . two . . . one. . . .”

BLOWIE!!!!!!

Gads! Geraldo and his blue boys had blown down a wall. And behind it stood . . . another wall.

Journalism is hell.

What was behind that wall? Forget it for now. Time again to glorify crime with a tape of famed Hollywood personality Buddy Rogers recalling a dinner he had with “my pal” Capone. “You thought of him as a co-celebrity, didn’t you, Buddy?” asked Rivera. “That’s right,” Rogers said.

And there was more, including co-producer Doug Llewelyn (Mr. Hair himself, who doubles as host of “The People’s Court”) at an “Al Capone Safecracking” charity ball.

Finally, back live, in the basement of the Lexington Hotel, Geraldo gathered his blue boys around him and sheepishly told America that they had only dirt to show for their efforts.

“What can I say? I’m sorry,” Rivera apologized. He was sorry? “All right. I’m goin’. I’m sorry. See ya next time.”

And just like that, he walked away down a dark tunnel, crooning “Chicago,” vanishing like, well, a thief in the night.

Writing in Esquire, Rivera faults “Establishment” reporters for their “one inviolable rule: never, ever get involved; never get down and dirty.”

In Chicago, Geraldo Rivera had showed his stuffy, musty colleagues how it’s done. He had gotten down, all right, and he had gotten very, very dirty.