Two would-be terrorists - allegedly recruited by Al Qaeda and carrying US passports - are believed to be behind the car bomb plot planned for Washington or New York on the 10th anniversary of 9/11, authorities said.

The "specific and credible" info about a plot involved three veteran terrorists approved by Al Qaeda chief Ayman al-Zawahiri, investigators told the Daily News.

The names of all the men are known to investigators, but they were too common to provide much direction.

A CIA tipster, who has provided credible information in the past, said that the men are of Arab descent and may speak both English and Arabic, according to the AP.

Intel analysts have been combing over travel patterns of people who recently entered the country, but they have yet to find any evidence that the terror plotters have entered the country.

While avenging the death of 9/11 mastermind Osama Bin Laden is a terrorist chatter staple, the intercept of an Al Qaeda operative's conversation did not characterize the bomb threat as a revenge attack, the investigators indicated.

The goal, sources said, was to commit mass casualties and mayhem for the memorial event.

During a morning meeting of his national security team President Obama promised to keep a breast of the nascent plot and urged his people to maintain a "heightened state of vigilance and preparedness" going into the anniversary.

Word of the possible terror hit cranked up security on city streets, subway platforms and train stations over the weekend.

Cops in the city and Long Island put out a related alert late last night for a white "Budget Rental" van with the Oklahoma tag 2LE922 stolen from Jersey City, 1010 WINS reports.

But a high ranking law enforcement source indicated that the pinched vehicle was not part of the terror scheme.

"There are alway stolen rental vans - the nature of the business," he said.

Still, the NYPD flexed its anti-terrorist muscles from the Bronx to the Battery, emphatically answering the unconfirmed terror plot.

"This is our version of Bush's shock and awe," said one NYPD official. "The idea is to scare off a sophisticated network - let alone three men."

Checkpoints around the city focused on vans with rental plates as the NYPD used license plate scanners and portable radiation detectors in its extensive efforts.

The high-security response, on the eve of this year's 9/11 memorial service, slowed Manhattan traffic to a crawl. Irked straphangers were stranded on buses, while infuriated fares sat in cabs.

"In more than 40 years, I've never seen this kind of all-out attention," said an NYPD lieutenant on patrol.

Cops were also operating under the radar, leaning on informants while keeping tabs on car and truck rental agencies - along with companies selling fertilizer and other bomb-making materials.

"A lot of the precautions we take, you can't see," Mayor Bloomberg said.

With John Doyle, Daniel Prendergast and Glenn Blain and News Wire Services

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