The interim chief of the new National Counterterror Center (search) said Thursday he is stepping down from his post later this year, leaving after the biggest intelligence overhaul in 50 years.

In a memo to his staff, John O. Brennan (search) said he had told National Intelligence Director John Negroponte (search) about his decision to retire, and offered to stay until a replacement is confirmed. He said his retirement "is in the best interest of my family."

"There are times in all of our lives when we must make difficult decisions about personal and professional futures," Brennan wrote in the memo, which was read to The Associated Press by a senior U.S. intelligence official. "I have reached such a point."

The center, located in an undisclosed location in Virginia, coordinates the nation's fight against terrorism by analyzing intelligence from 15 independent spy agencies and law enforcement officials in state and local government.

It opened as part of wide-ranging intelligence reforms, approved in December, that were spurred by what critics called a government failure to collect, understand and share critical information before the Sept. 11, 2001 terror attacks.

Brennan, a 25-year CIA veteran and Middle East expert, headed the joint CIA-FBI Terrorism Threat Integration Center (search) that briefly served as a precursor to the counterterror center. He also delivered the President's Daily Brief — the CIA's 24-hour rundown of intelligence data — during the Clinton administration.

A spokesperson for Negroponte, who started his job in April, said Brennan "has had a distinguished career in the intelligence community."

"We are very pleased he will continue to offer his expertise to advance the mission of the U.S. government counterterrorism community," the spokesperson said.