BOSTON — Five years after the terrorist attacks of Sept. 11, 2001, human intelligence and systems that quickly gather and distribute information from satellites and other platforms have become major priorities. While little has changed about the fundamental role of imaging satellites, some major changes could make them more relevant to the hunt for terrorists around the world, according to several national security experts.

The use of imaging satellites for intelligence gathering to combat terrorism has not changed much since U.S. passenger aircraft crashed into the World Trade Center, the Pentagon and a field in Pennsylvania on Sept. 11, 2001. They are employed in a manner that effectively monitors large military and industrial facilities, but is less effective in combing the landscape for small groups of terrorists, according to several experts inside and outside the government who were interviewed for this article.

The inherent weakness of the imagery satellites in low Earth orbit is that they spend far too much time out of position and are too easily evaded based on publicly available information about their orbits, the experts said, noting that those weaknesses kept imaging satellites from playing a major role in finding high-value targets like Osama Bin Laden and Taliban leader Mullah Mohammed Omar, the experts say.

Improving the way satellites are used in the war against terror starts on the ground, they said. Imagery satellites today are too often given a static set of instructions to monitor particular areas of interest, with few changes made on a regular basis, according to a congressional aide.

Addressing this problem does not necessarily require the development of new types of satellites, the aide said.

Instead, m odifications are needed to ground systems that will enable those in the field to quickly instruct a satellite to look at a different spot in response to a new lead in the search for terrorists, the aide said.

While the intelligence community has started to embrace this type of thinking, there is some resistance from officials who are reluctant to change the way spy satellites have been used since the government began launching them decades ago, the aide said.

Information about terrorists that is collected by satellites must be processed and distributed much faster, the experts said. In this case, they noted, there is clear evidence that the government is addressing the issue. Don Kerr, director of the National Reconnaissance Office, issued a memorandum in April to his agency calling for a greater emphasis on ground-based data handling and processing systems. Kerr’s memo states that newly available processing technology could produce major capability breakthroughs for military and intelligence users.

James Lewis, senior fellow and director of the technology and public policy program at the Center for Strategic and International Studies, a Washington-based think tank, said the National Geospatial-Intelligence Agency has made some improvements using software to fuse satellite imagery with data from other sensors as well as information that can be gleaned through open sources.

Signals intelligence satellites that can eavesdrop on terrorist communications from geostationary orbit do not have the same difficulty that low Earth orbiting imagery satellites face in staying in position to monitor terrorist groups, said Michael O’Hanlon, a senior fellow in the foreign policy studies department at the Brooking Institute, another Washington-based think tank. However, senior U.S. government leaders might have spoken too openly in 2001 about their ability to locate Osama Bin Laden in Tora Bora, Afghanistan, and only the least sophisticated of terrorists are now likely using communications lines that can be monitored by signal intelligence systems, he said.

Despite the difficulties that imagery satellites might have in tracking terrorists, their importance to national security should not be overlooked, O’Hanlon said. The need to fight terrorists has not eliminated the need to monitor countries like China, Iran and Russia, he said, and in some cases, using satellites to keep tabs on facilities in those countries may help to curb the proliferation of weapons of mass destruction to terrorist groups.

Though questions may exist about the utility of imagery satellites for the intelligence community’s work in tracking terrorists, Lewis noted that the satellites have played an increasing role for tactical forces on the battlefield.

Loren Thompson, chief operating officer of the Lexington Institute, a think tank based in Arlington, Va., called satellites possibly “the least appropriate way” of tracking terrorists.

“Osama, and other senior Al-Qaeda leaders like [Ayman al-] Zawahiri, are still at large — no one on Sept. 12, 2001, would have guessed that would be the case,” Thompson said.

Thompson said that terrorists may present a target too fleeting to follow with satellites, and said he sometimes wonders whether some of the money currently planned for next-generation imagery satellites would be better utilized if it was diverted to accounts for more human intelligence.

Thompson said that his lack of confidence in imagery satellites to find terrorists does not mean that he does not believe space is part of the picture. Communications satellites, particularly next-generation systems that will pass more information at much faster rates, will play a key role in this battle, he said.