In another blow for beleaguered BlackBerry maker Research In Motion, the U.S. federal government's main procurement agency is issuing iPhones and Android-based devices to some of its 17,000 workers.

While the General Services Administration does not impose its purchasing decisions on other parts of the government, the terms and conditions it negotiates can be used as a blueprint for other agencies.

We actively seek to be progressive in our adoption of new technologies so that we can learn the lessons which will inform our client and customer agencies as they seek to go down a similar path, the GSA's chief information officer, Casey Coleman, told Reuters in a phone interview on Tuesday.

Once Washington's only option for secure mobile communication, RIM has struggled to offset a rising tide of companies allowing their workers to use their own devices for work or supplying them with rival devices, which have made strides towards matching the BlackBerry's famed security.

The GSA - which manages $500 billion of government assets including telecom, information technology and real estate - is also testing the use of employees' personal smartphones and tablets on their secure networks, a popular move for corporations looking to cut costs.

Coleman said that BlackBerry remains by far the most used smartphone at GSA, with devices from Apple and those using Google's Android software accounting for less than 5 percent of the agency's fleet, which covers the majority of GSA employees.

The personal smartphone pilot is to supplement rather than replace government-issued devices, she said, and the GSA has no plans to abandon RIM servers, which manage secure BlackBerry traffic.

RIM charges a fee for use of its servers and data centers, which compress and encrypt email and other sensitive data.

The GSA's move is just the latest hurdle to face Waterloo, Ontario-based RIM.

Another U.S. agency, the National Oceanic and Atmospheric Administration (NOAA), said last week it would ditch the servers that run its BlackBerrys by June as it trimmed costs.

Oilfield services company Halliburton plans to switch 4,500 BlackBerry-toting employees to iPhones, saying it's is better suited to its needs. Several banks have also welcomed BlackBerry rivals.

The NOAA move was made possible after it switched its desktop-based software to Google Apps for Government.

Coleman said the GSA moved to Google Apps in June, cutting its costs in half compared with its legacy desktop software.

The GSA plans to offer a service so other agencies can quickly order Web-based email, she said.

This is an area that is changing and evolving rapidly and as the market changes we will continue to seek to provide our employees with the best devices for them to do their best work.

(Reporting by Alastair Sharp; editing by Rob Wilson)