HE'S THE Joe Namath of Doomsday hucksters, but the stakes are much higher than Super Bowl III.

Harold Camping, the 89-year-old Christian evangelist from Oakland whose Family Radio broadcasts are heard in 61 languages, doesn't think that Judgment Day will come Saturday. He guarantees it.

"It is absolutely going to happen," said Camping, who has determined after five decades of studying Scripture that May 21 marks the beginning of the end. "We do not have a Plan B at all. There is no possibility that it will not happen, because all of our information comes from the Bible."

So if you haven't made amends with God, cancel your weekend plans, Camping says.

Forget about Phillies vs. Rangers at Citizens Bank Park on Saturday. Disregard the five-day forecast. And it doesn't matter whom you vote for in today's primary. The candidates aren't going to make it to the general election in November.

No one will.

The earthquake that rocked Japan in March will be a mere seismic blip compared with the cataclysmic earthquake that will rumble across the planet on Saturday, reaching Philadelphia about 6 p.m., according to Camping and his legion of followers from here to China.

Millions will die on the first day and an earthquake "such as was not since men were upon the Earth" will "throw open all graves" as the remains of the believers are "instantly transformed into glorified spiritual bodies to be forever with God," Camping has written in his brochures.

And you unrepentant sinners? Prepare to live in a world of "horror and chaos beyond description" that will last until Oct. 21, when everyone and everything will be wiped out completely.

"Until the Day of Judgment begins, God teaches us that he's still saving people," Camping said in an interview this week. "Cry out to God, 'Oh, Lord, have mercy! Maybe you could still save me.' Keep begging him."

We know what you're thinking: Camping is a certified nut job. Preachers have been ranting about fire and brimstone for nearly two millennia. Anyone can stand on a street corner and predict that the end is nigh.

But this is different. Billboards have been erected around the globe. SEPTA buses are wrapped in Camping's prophecy. Soccer moms have turned their minivans into rolling advertisements. There are bumper stickers. T-shirts. Lawn signs.

"It's the greatest ad campaign in the world," said Robin Harp, 66, a former factory worker who drives a van covered with the Family Radio message. "God's coming to bring judgment, and this earthquake will be like no other earthquake. You want to warn those you love."

People believe Camping's biblical calculations. A lot of people. Normal people. Educated people.

Like Ralph Workman, 50, of Landenberg, Chester County, an engineer at Boeing's Delaware County helicopter plant and a Family Radio caravan manager. He organizes a crew that spreads Camping's message in the hope of saving souls.

"People think we're a bunch of crazy coots, but we have a lot of educated people," said Workman, an even-keeled guy who's quick with a smile and patient with skeptics.

Workman runs down a list of sane believers, including a former commercial airline pilot, a medical doctor, a college professor and a mathematician.

"I'd be doing this full time if not for my wife," Workman said, with his sons, ages 10 and 12, by his side - and on his side of the debate. "She doesn't believe it and doesn't want to hear about it, but we're absolutely certain.

"Yep," he said of his sons. "They both believe. I'm very proud of them."

Workman was among about 150 Judgment Day believers gathered in the basement of a Delaware County union hall for the "last Sunday" meeting of the eBible Fellowship, one of the many groups that are promoting Family Radio's message.

You might expect the place to be full of brainwashed freaks like the Heaven's Gate cult, whose members strapped on brand-new Nike sneakers and committed mass suicide in 1997 so they could board a UFO.

Or maybe you'd find them speaking in tongues or handling snakes. Because, let's face it, history has shown that Doomsday prophets are often deranged and always wrong.

Instead, the union hall was full of diverse and rational people who happen to believe in something completely irrational. They sipped coffee and munched on Dunkin' Donuts. They just want to save you.

"People are very concerned about us," said Chris McCann, 49, of Darby Borough, who runs eBible Fellowship. "They're worried we're going to drink the Kool-Aid. They're worried there's going to be a mass suicide.

"However, when the vast majority of people in the world do not take heed, and they're not listening to God, what have they done to themselves when May 21 comes?" he asked the audience. "They've killed themselves."

McCann knows that much of the world is laughing at him. But he fully expects to laugh last as he's whisked away to Heaven while the sinners face God's wrath. "The concern is not, 'What are we going to do when it doesn't happen?' " he said. "It's 'What are you going to do when it does?' "