Peterson says that many agencies will have to work with limited funding, even in cases where they can demonstrate clear benefits from moving to the cloud.

"Budget constraints and a lack of resources are always in the mix of being top concerns or challenges," says Tim Herbert, vice president of research at the Computing Technology Industry Association (CompTIA), which has surveyed government IT leaders on subjects such as cloud computing. Other issues that could slow or halt the move to the cloud include slow-moving bureaucracies, fear of change, lack of interoperability between legacy and cloud-based systems, the challenge of coordinating technologies across agencies, and a lack of skilled personnel, he says.

In MeriTalk's recent study, 79% of the federal CIOs polled said budget constraints are a top obstacle to implementing cloud computing, and 71% said security concerns are preventing cloud adoption. Some of those issues could also influence what model of cloud computing -- private, public, community or hybrid -- federal agencies adopt.

Some agencies are large enough to build their own private clouds and still reap financial benefits, Peterson says. But many others are too small to handle such a move and wouldn't see any cost benefits from doing so. That's not to say, however, that there isn't a potential for big savings with private clouds. Peterson points out that large agencies could build private clouds and then sell capacity to smaller agencies under a shared-services model.

But for that model to work and produce a strong ROI, government entities would have to move beyond their often parochial outlooks and build a culture that embraces cross-agency cooperation, say Peterson and other analysts.