FACTBOX: Breaking down the U.S. counterterrorism bureaucracy

(Reuters) - President Barack Obama has summoned U.S. intelligence, counterterrorism and homeland security chiefs to a White House meeting on Tuesday to discuss how to prevent a repeat of the attempted bombing of a passenger jet on December 25.

Turf battles between within the U.S. counterterrorism bureaucracy are nothing new. But lapses that allowed a Nigerian suspect to board a Detroit-bound plane with a bomb on Christmas Day, and the finger-pointing that followed, have raised questions about sweeping changes made to improve security and intelligence-sharing since the Sept 11, 2001, attacks.

Here are the lead U.S. government agencies in intelligence, counterterrorism and homeland security, and a description of the roles they play:

OFFICE OF THE DIRECTOR OF NATIONAL INTELLIGENCE

Serves as head of the intelligence community and as principal adviser to the president on intelligence matters. The Office of the Director of National Intelligence, Dennis Blair, is ultimately responsible for integrating foreign, military and domestic intelligence. Blair and CIA Director Leon Panetta have squabbled for months behind-the-scenes over the DNI's oversight role. Officials say 2004 legislation overhauling the intelligence system left some of the DNI's authorities vague.

CENTRAL INTELLIGENCE AGENCY

CIA Director Leon Panetta reports to the Director of National Intelligence. The CIA oversees and carries out clandestine operations around the world. Seeking to ease tensions between the DNI and the CIA over turf, the White House recently brokered a deal under which the CIA will keep Blair's office informed about its secret activities, intelligence officials said.

NATIONAL SECURITY AGENCY

An intelligence powerhouse that intercepts and monitors communications overseas. It is headed by Lieutenant General Keith Alexander. The agency answers to the Secretary of Defense and the Director of National Intelligence.

NATIONAL COUNTERTERRORISM CENTER

Established in 2004 to serve as the main processing center for counterterrorism intelligence gathered by more than 16 government agencies, including the CIA and the National Security Agency. The center had intelligence about the would-be bomber but did not "connect the dots." Michael Leiter is the center's director.

FEDERAL BUREAU OF INVESTIGATION

Since the September 11 hijacked-plane attacks, the FBI has shifted to focus more on pursuing terrorism threats and suspects, domestically and internationally. As a result, FBI Director Robert Mueller has set up 65 new Joint Terrorism Task Forces designed to investigate threats, gather evidence and intelligence as well as share information with various other national, local law enforcement and intelligence agencies. It has agents assigned to the National Counterterrorism Center.

DEPARTMENT OF HOMELAND SECURITY

President George W. Bush created a special Office of Homeland Security in response to the 2001 attacks. In late 2002 Congress approved the creation of a new department to focusing on protecting the United States, now headed by Janet Napolitano. A massive agency with some 225,000 employees, it includes a focus on security for the U.S. borders, transportation systems and cybersecurity. It includes the U.S. Coast Guard, Transportation Security Administration, Secret Service, U.S. Customs and Border Protection and U.S. Immigration and Customs Enforcement.

TRANSPORTATION SECURITY ADMINISTRATION

The TSA was created soon after September 11 to replace private-sector screeners who were employed by the airlines and criticized for lax inspection practices. TSA is responsible for checking passengers and luggage. It also includes federal air marshals who travel on some U.S. and foreign flights in an effort to detect and combat potential attacks. It has been widely criticized by travelers for issuing confusing instructions on screening procedures and on security measures aboard flights. Obama's choice of Erroll Southers to head TSA has been held up by a Republican senator.

(Reporting by Adam Entous and Jeremy Pelofsky; Editing by Patricia Wilson and Jackie Frank)