FACTBOX: Security for Obama's inauguration

(Reuters) - An unprecedented security operation is under way in and around Washington for Barack Obama's inauguration as the United States' first black president on Tuesday.

Following are a few facts and figures about the steps being taken:

* The Homeland Security Department says there is no credible threat of an attack but they are prepared for a wide range of potential catastrophes, including a chemical weapons attack.

* The Secret Service, responsible for protecting the president, is overseeing the security preparations. Director Mark Sullivan, a 25-year veteran, says Tuesday's inauguration is the biggest event he has been part of.

* About 4,000 city police officers will be deployed along with 4,000 from 96 other law enforcement agencies across the country. Members of the Secret Service, FBI and Capitol Police will also be on duty.

* A total of 32,000 military personnel will be on duty or on standby.

* Security measures include intensified patrols of the skies over the capital and rivers bordering the city, closing bridges and sealing off a large area of downtown to vehicles.

* The Secret Service has unveiled a state-of-the-art armored presidential limousine that Obama will use during his presidency. Its design is a closely guarded secret, but it is likely resistant to bomb and chemical attacks.

* Every one of the hundreds of thousands of people expected to pack the inaugural parade route between the White House and Capitol Hill will be subjected to security screening, as will the 240,000 people attending the swearing-in ceremony.