WASHINGTON (Reuters) - President Barack Obama’s pledge to seek a worldwide ban on weapons in space marks a dramatic shift in U.S. policy while posing the tricky issue of defining whether a satellite can be a weapon.

A man walks through an exhibition in the former "Vengeance Weapon 2" rocket testing site in Peenemuende, March 7, 2008. REUTERS/Tobias Schwarz

Moments after Obama’s inauguration last week, the White House website was updated to include policy statements on a range of issues, including a pledge to restore U.S. leadership on space issues and seek a worldwide ban on weapons that interfere with military and commercial satellites.

It also promised to look at threats to U.S. satellites, contingency plans to keep information flowing from them, and what steps are needed to protect spacecraft against attack.

The issue is being closely watched by Lockheed Martin Corp, Boeing Co, Northrop Grumman Corp, the biggest U.S. defense contractors, and other companies involved in military and civilian space contracts.

Watchdog groups and even some defense officials welcomed the statement, which echoed Obama’s campaign promises, but said it would take time to hammer out a comprehensive new strategy.

Enacting a global ban on space weapons could prove even harder.

For instance, it was difficult to define exactly what constituted a “weapon” because even seemingly harmless weather tracking satellites could be used to slam into and disable other satellites, said two U.S. officials involved in the area who were not authorized to speak publicly.

Michael Krepon, co-founder of the private Henry L. Stimson think tank on space, cited recent reports that the Pentagon was using two smaller satellites launched in 2006 to fly near a dead missile-warning satellite and investigate what happened. The Defense Support Program satellite, DSP-23, built by Northrop, failed on orbit in mid-September.

“This incident clarified how important it is to have rules of the road for technologies that could have many different applications,” Krepon said. “There are lots of benign reasons to have a closer look at an object in space. But we all know that when satellites make close passes they could also do things that are not benign.”

Two years ago, China used a missile to destroy one of its own satellites in a test that raised worries about a new arms race in space. The incident may have created thousands of pieces of debris. Last year, the United States also destroyed one of its own satellites, saying its toxic fuel tank could pose a danger if it fell to Earth.

MORE COOPERATION?

A defense official, who also asked not to be named, said the Obama administration had not yet held briefings for top officials working on military space issues, but it was clear that the focus would shift toward more diplomatic initiatives.

Work on classified projects involving an “active” military response to attacks against U.S. satellites might be halted in favor of more monitoring and passive protection measures, he said. He declined to give any more details.

The Obama administration also faces tough decisions on many multibillion-dollar satellite programs facing cost overruns and schedule delays, particularly at a time when rapid increases in military spending are grinding to a halt.

“There’s still a lot of wiggle room” in the administration’s statement on military space, said analyst Victoria Samson with the private Center for Defense Information. “But just the sheer fact that they are discussing it represents a real shift from the Bush administration.”

“It’s not going to happen immediately, but it seems as though the wheels are in motion to initiate some sort of cooperative measure,” Samson said.

Another defense official, who asked not to be named, said the new administration would work through the complex military space issues during a defense review to be completed by September, and as part of a space report due in December.

The new policy language used by the Obama administration was “impossibly broad,” the official said. It also failed to acknowledge recent work by U.S. officials on guidelines for space debris and conduct by nations active in space.

Even Obama acknowledged during his election campaign that achieving a global treaty banning weapons in space could be a daunting challenge. A simpler and quicker solution, he suggested at that time, might be a “code of conduct for responsible space-faring nations.”

In response to questions from the Council for a Livable World, Obama said one key element of any such code would be “a prohibition against harmful interference against satellites.”