It’s a good thing Osama wasn’t walking through SoHo yesterday morning.

Two sets of confidential blueprints for the planned Freedom Tower, which is set to rise at Ground Zero, were carelessly dumped in a city garbage can on the corner of West Houston and Sullivan streets, The Post has learned.

PHOTOS: WTC Blueprints Found In Trash

Port Authority’s News Blackout Is Sinister

Experts said the detailed, floor-by-floor schematics contain enough detail for terrorists to plot a devastating attack.

“Secure Document – Confidential,” warns the title page on each of the two copies of the 150-page schematic that a homeless, recovering drug addict discovered in the public trash can.

“Any time a sensitive document is unintentionally left behind, it’s a treasure trove for a potential adversary,” aid Robert Strang, CEO of Investigative Management Group, a global security firm. “It enables them to look for vulnerabilities in design that they can target – an age-old military tactic.”

Informed of what the homeless man, Mike Fleming, had found, shocked Port Authority officials called it an egregious security lapse.

“Violating these protocols is cause for serious disciplinary action – up to termination for employees and breach of contract and legal action for contractors,” said Candace McAdams, PA director of media relations.

One of the identical sets was missing the first 14 pages, which is particularly alarming.

Besides the PA, there are 11 entities listed on each page of the blueprints, including the builder, Tishman Construction, and architects Skidmore Owings and Merrill.

Although the documents, dated Oct. 5, 2007, are not a complete set of blueprints, they do contain details such as plans for each floor, the thickness of the concrete-core wall and the location of air ducts, elevators, electrical systems and support columns.

“Certainly, if you know the thickness of concrete, someone with an explosive background can develop and plot an attack,” Strang said.

That was exactly the thought that ran through Fleming’s mind when he found the documents and alerted The Post.

Fleming, 28, originally from Ohio, said he was rummaging through the garbage in search of cardboard, “because the concrete is so cold to sleep on,” when he noticed the documents and the warning to “properly destroy if discarded.”

“They were right on top, and the garbage truck came along 10 minutes later,” he said. “I was outraged, because this is priceless and it could gets into the wrong hands.

“I am an honest guy. This could have ended up on eBay or gotten to al Qaeda.”

The schematics were distributed to PA officials, architects and contractors, and the state’s inspector general will be investigating who improperly disposed of the sensitive materials, which the agency had no intention of making public, McAdams said.

“We don’t tolerate carelessness and stupidity, which is why we have these strict protocols in place,” she said.

According to McAdams, the plans are several versions old, “not very detailed” bidding documents that are given to anyone bidding on contracts.

But Steve Yang, an architect who reviewed the schematics for The Post, said that even though they do not contain every detail, it would be easy to fill in the blanks.

“An expert in explosives, demolition or biological weapons certainly could glean enough here to develop a game plan,” he said. “You can see where all the concrete walls are, where the emergency stairwells are, and the electrical and HVAC systems.”

The air-intake and ventilation systems in most modern office buildings would make it extremely difficult to cause widespread damage with a gas or anthrax attack, thanks to the filtration systems, a security source said.

Security sources say that such breaches tend to be inside jobs and that the garbage-can drop might have been intentional.

“The insider threat is always a corporation’s biggest threat, and a terrorist adversary will try to locate disgruntled employees,” a security-industry source said.

Relatives of 9/11 victims say that lapses in security over Ground Zero have ceased to be surprising.

“I’d certainly be pretty leery going to work in the building knowing that security on the plans was so lax that even a vagabond could find them,” said Bill Doyle, whose son, Joseph, was killed in the Twin Towers.

“The whole thing is kind of frightening, but at the same time totally expected, because we have been failed time and again.”

As shocking as such dangerous lapses in security are, experts contend that they are bound to happen again.

“Outrageous security breeches like this amplify how vulnerable New Yorkers are,” said Nicholas Casale, former head of security for the MTA.

Additional reporting by Murray Weiss

jeremy.olshan@nypost.com