High Alert in Delhi as Obama Arrives for Republic Day

Indian, US security services coordinating closely for trip.

NEW DELHI, India— -- U.S. and Indian security agencies and intelligence services are mounting an unprecedented operation to keep President Obama safe on foreign soil as he arrives here for a historic visit as "chief guest" of Republic Day.

Security is always tight wherever the U.S. president goes, but it appears that measures have been taken to a new level for this trip.

Driving it all is the fact that Obama will spend a several more than two hours outdoors Monday on an open-air viewing platform in the center of the city -- a situation Secret Service tries very hard to avoid.

The situation is made more complicated because foreign military aircraft will be crisscrossing overhead, tens of thousands of residents are expected to be clogging surrounding streets -- and escape routes, and Pakistani militants have been threating terror.

"There's not been a similar event that he's attended overseas," deputy national security adviser Ben Rhodes said. "So this is unique."

Obama's Legacy Turn: From Yes We Can to Yes We Did

The memory of the September 2008 series of deadly coordinated bombings around Delhi is fresh on peoples' minds. So, too, is the assault on a Mumbai hotel by alleged Pakistani militants two months after the Delhi bombing.

India's top military officials have warned in recent days of potential terror strikes by Pakistani militants against soft targets in and around New Delhi, a threat Pakistan denies.

The Secret Service and its Indian counterpart are not taking any chances.

There will be more than 80,000 Indian police and paramilitary officers in the streets, officials say.

At least 15,000 closed-circuit TV cameras have been installed to watch the crowds.

Every inch of the parade route has been scouted for pre-planted bombs. ABC News observed agents probing shrubs, bushes and manholes. They were followed by bomb-sniffing dogs.

A city trying desperately to clean up its image has even overturned thousands of trash cans within a mile radius around the ceremonial area, which is also lined with steel fence.

Everyone entering the secure zone will be magged and frisked for no less than 15 seconds, local officers have been told.

An Indian AWACS plane will for the first time be watching all of this from above, monitoring any incoming projectiles or errant aircraft.

And while Indian security forces turned down U.S. demands for their snipers, they will for the first time let their chief guest arrive to the viewing stand in his own car, the armored Cadillac known as "The Beast" -- which Washington said was was non-negotiable, ABC News was told.