The director of the National Security Agency and his deputy are expected to depart in the coming months, US officials said on Wednesday, in a development that could give President Obama a chance to reshape the eavesdropping agency.

Army general Keith Alexander's eight-year tenure was rocked this year by revelations contained in documents leaked by former NSA contractor Edward Snowden about the agency's widespread scooping up of telephone, email and social media data.

Alexander has formalized plans to leave by next March or April, while his civilian deputy, Chris Inglis, is due to retire by year's end, according to US officials who spoke on condition of anonymity.

One leading candidate to replace Alexander is Vice Admiral Michael Rogers, currently commander of the US navy's 10th Fleet and US Fleet Cyber Command, officials told Reuters. The 10th Fleet and Fleet Cyber Command both have their headquarters at Fort Meade, Maryland. The NSA is also headquartered at Fort Meade.

There has been no final decision on selecting Rogers to succeed Alexander, and other candidates may be considered, the officials said.

An NSA spokeswoman had no comment on the leadership changes.

Alexander has served as NSA director since August 2005, making him its longest-serving chief. He also serves as commander of a related military unit, the US Cyber Command.

Alexander, who has vigorously defended the NSA's activities as lawful and necessary to detect and disrupt terrorist plots, has previously said he planned to leave in the spring.

Inglis, who began his NSA career as a computer security scientist, has been the NSA's second-ranking official since 2006.

While both men are leaving voluntarily, the dual vacancies give Obama an opportunity both to install new leadership following Snowden's revelations and to decide whether the NSA and Cyber Command should have separate leaders.

Cyber Command, which has grown significantly in recent years, has the authority to engage in both defensive and offensive operations in cyberspace. Many NSA veterans argue that having the same person lead the spy agency and Cyber Command diminishes the emphasis on the NSA's work and its unique capabilities.

Alexander is the very definition of "by any means necessary".