BlackBerry’s last stronghold in the smartphone market may be under siege.

A review of Apple and Samsung’s software for use on the Defense Department’s secure classified and unclassified networks is expected to be completed within two weeks and could further curtail BlackBerry’s once dominant position among the security-conscious government employees.

The Defense Department may allow its employees to choose among Samsung and Apple smartphones and tablets for the office, according to a statement from the agency.

BlackBerry is already on the defensive. It is trying to win back customers — it lost 3 million during the last quarter alone — with new smartphones designed to appeal to fans who crave modern smartphone features but need the security that has kept BlackBerry in the good graces of many businesses and government clients.

Its new operating system, BlackBerry 10, received approval from the department Thursday.

Meanwhile, the consumer success of tablets and smartphones running Apple’s iOS or Google’s Android operating system has begun spilling into the business and government markets as more employees have used their personal devices at the office.

Those devices have also become commonplace on Capitol Hill and in the halls of the State Department, NASA and the Department of Homeland Security, which have given their employees approval to use iPhones, iPads and Android devices.

BlackBerry still has a majority of the overall business market despite delays that kept customers waiting for devices with faster browser speeds and a lack of apps. But even that market may be starting to slip away — according to the International Data Corp. research firm, Apple was on pace to ship the most devices for business use in 2012.

Although the review process could give Defense employees the option of using Apple and Samsung devices, it’s not a guarantee of greater sales. The approvals “do not directly result in product orders but facilitate the process by eliminating the need for security reviews at the individual DoD organization level,” a department spokesman said in a statement.

Apple and Samsung declined to comment on the review process. BlackBerry did not immediately respond to requests for comment.

Related stories:

DOD opens up to more commercial mobile devices

Samsung sets sights on corporate customers

BlackBerry 7 models approved by Defense

Sign up today to receive #thecircuit, a daily roundup of the latest tech policy news from Washington and how it is shaping business, entertainment and science.