Concerned that sensitive information might leak out, some units of the United States military are starting to clamp down on e-mail communication from their soldiers and sailors, who have been using it from ships, major bases and even desert outposts around Iraq to stay in touch with family and friends.

The uncertainty underscores the double-edged nature of a technology that is giving an unprecedented opportunity for instantaneous interaction from the most remote locations, a development the Pentagon believes is helping to improve the morale in the field and at home. At the moment, much of the electronic communication is going unmonitored by the military, providing an opportunity for what some fear could be inadvertent leaks from the potential battlefield.

The air force warned last week that it might limit or start blocking electronic messages because some people had sent home sensitive information, including digital images that might have compromised unit safety. The navy has said that on submarines, it is monitoring all e-mail traffic. And the army, while generally maintaining open access to e-mail, is restricting some Internet connections from certain bases.

Across the military, individual soldiers have been instructed not to send sensitive information. But the policy about what Internet access to allow and what material to monitor or censor has been largely left to division and unit commanders on the theory that they are best able to judge what constitutes a real threat to security.

Some military critics argue that there should be a clearer Pentagon-wide policy on how to deal with a communications system that offers instant access beyond what was available in any previous conflict. The critics assert that e-mail and Internet communication raises several potential problems: It is voluminous and thus hard to monitor; it can convey not only words but images; and it is immediate, meaning that an enemy could conceivably tap into real-time updates of, say, troop movements, the presence of a general, or a military outpost's perimeter defenses.

Still, computer security experts are not particularly concerned that Iraqi forces would devote much attention to trying to hack into e-mail communications from U.S. troops. Moreover, the military's sensitive operational information is kept on a proprietary network called the Secret Internet Protocol Network that is not connected to the publicly-accessible Internet, making it extremely hard for hackers to penetrate.

Rather, the problem that computer and military experts worry about is that Iraqi forces might accidentally obtain a message sent home by a soldier that ended up being forwarded to someone sympathetic to Iraq, or that outsiders might view a picture published on a publicly accessible Web site.

"The timeliness of the information is a major factor, and the volume of message traffic can be very dangerous," said Keith Eiler, a military historian at the Hoover Institution at Stanford University. "It's a potentially serious problem and not one that is easily solved."

Eiler said he would like to see a clearer policy, and perhaps some monitoring and censorship of communication, as was the case with letters in World War II and Korea, and to an extent with mail and even telephone calls from Vietnam.

Electronic connections bring an ease of communication not even seen in the Gulf War, which took place before the widespread commercial use of the Internet and e-mail.

"It's more wonderful than you can imagine," said Gary Richardson, a consultant in Napa, California, whose 32-year-old daughter, Patricia, is in an army battalion at an undisclosed overseas location. "When you get a message, you know that her hands were just on the keyboard and that she was alive and well just a few minutes ago."

The computer technology also brings soldiers a slice of home. Major Richard Patterson, the public affairs officer for the army's 82nd Airborne, brought a Web camera with him to his post in Bagram AirField in Afghanistan. Using the camera, he participated in a video conference over the Internet with his family, which allowed him to witness his daughter's first birthday.