M By Steve Vogel

ilitary aircraft equipped with sophisticated sensors far more sensitive than those used by police will join in the hunt for the sniper terrorizing the Washington area, Pentagon officials said Tuesday.

The aircraft will use aerial surveillance tools with night vision to “put eyes on the target very, very quickly,” even if the gunman should strike under cover of darkness, a senior military officer said.

The decision to use the military in a domestic criminal case, while not unprecedented, is highly unusual and reflects the gravity of the search for the sniper who has killed nine people and wounded two others since Oct. 2.

“We all share the sense of urgency in trying to stop this,” said a defense official, speaking like others on condition he not be identified.

Among the concerns raised is whether such assistance would violate the Posse Comitatus Act, the 1878 law that bars the military from performing civilian law enforcement.

The authorization, signed Tuesday by Secretary of Defense Donald Rumsfeld, is within the law, Pentagon officials said. Military pilots would be accompanied by federal agents during surveillance flights, officials said.

“Military operators would be doing that – just operating the equipment,” said a senior Pentagon official. “Law enforcement would do the analysis and follow-up.”

If the aircraft sensors detected a muzzle flash from a gun, for example, it would be up to the civilian law-enforcement agent to interpret the data, another military official said. The aircraft also would help coordinate communication among law-enforcement agencies, officials said.

The military has manned aircraft equipped with electro-optical systems able to perform surveillance missions over a large area day and night. Computer-stabilized telescopic lenses aboard the aircraft are able to greatly magnify features.

“All of this goes well beyond what local police have,” said John Pike, director of globalsecurity.org, a defense think tank.

Defense experts said the Pentagon has other capabilities that may be of use in the investigation, including counter-sniper technology and expertise.

The Defense Department has counter-sniper equipment able to detect heat from muzzle flashes and the sound of a gun firing and to locate the source of the fire almost instantaneously.

While effective, such equipment operates over a relatively short range.

“Trying to completely blanket the area would be very difficult,” Pike said.

Military experts on sniping and terrain analysis could help police predict where the sniper might strike next.

“It’s reasonable to assume that perpetrator is scouting sites in advance and using certain criteria,” Pike said.

Senior military officers worried Tuesday that the use of military tools in a criminal investigation could spark further requests for help in other notorious crimes while U.S. troops are in Afghanistan and gearing up for possible war with Iraq.

“The concern among the military is we’re not a domestic law-enforcement agency,” said a senior Pentagon officer. “We have a lot of equipment that I would want, too, if I were a police chief, but it’s the same equipment we need to fight a global war on terrorism, as well as Iraq.”

The Pentagon considered using an unmanned aerial vehicle such as the Predator, a defense official said, but the option was rejected because of the crafts’ heavy use overseas.

The request for military assistance came from Montgomery County, Md., and the FBI, a Pentagon official said. Officers on the staff of Air Force Gen. Richard Myers, chairman of the Joint Chiefs of Staff, contacted the military services Monday night and “asked, What do you have available that would be of assistance?” a senior officer said. Rumsfeld was briefed on the options Tuesday.

Federal troops have been used occasionally through U.S. history in domestic law-enforcement roles, including putting down the Whiskey Rebellion in 1794, integrating schools in Little Rock in 1957 and restoring order in Los Angeles during riots after the Rodney King verdict in 1992.

Under the terms of Posse Comitatus, the military can provide equipment and supplies, technical assistance and training to domestic law-enforcement agencies, said Eugene Fidell, president of the National Institute of Military Justice.

Fidell said the Pentagon assistance to the sniper investigation may go beyond that.

“I would have to say that active use in a search would raise a question,” Fidell said.

A U.S. District Court in New York held in 1961 that the use of an Air Force helicopter to search for an escaped prisoner was improper, he noted.