WASHINGTON -- President Clinton called Iraq's bluff on the Kuwaiti border with the help of a fleet of U.S. spy satellites even bigger and sharper-eyed than those President George Bush depended on four years ago.
Six satellites -- two more than Mr. Bush had -- now soar over Iraq twice a day, probing the earth through sunlight, darkness and clouds.
Last week, they beamed back detailed images that convinced the United Nations that Iraqi forces were moving south again. This week, they may help to settle doubts about whether the troops are really pulling back to the north or simply repositioning.
Still, the billion-dollar satellites -- originally developed to serve as space-based sentries against Soviet aggression -- are an expensive and sometimes clumsy tool to use in small-scale crises in the post-Cold War world.
As a result, the White House and the Pentagon depend as much, or more, on other sources of intelligence, including human agents on the ground, intercepted radio signals and low-flying -- reconnaissance airplanes.
Gen. John Shalikashvili, chairman of the Joint Chiefs of Staff, acknowledged yesterday that high technology failed to give the United States warning of Iraqi President Saddam Hussein's latest moves.
The Pentagon first learned about the Iraqi troop movements last Wednesday at "about the time" they were publicly disclosed by an Iraqi opposition group, General Shalikashvili said.
Even though they have been improved since the Persian Gulf war, spy satellites have their limitations. They can distinguish objects as small as a softball, but their field of vision is narrow. A standard image covers a rectangle about 6 miles wide and 10 miles long. Indeed, the code name for the current series of picture-taking satellites is KH, for "keyhole."
"It's like looking at the world through a soda straw," said John Pike, director of the Space Policy Project for the Federation of American Scientists.
He estimated it would take three to four days' worth of satellite snapshots to produce a composite image of the entire Kuwaiti operations zone. An airplane could cover that area in an hour.
Airplane reconnaissance is less glamorous but in some cases superior to space-based systems, military experts say. Indeed, Mr. Clinton dispatched two highflying U-2 spy planes to the gulf region last weekend to add to the existing force of airborne monitors.
Mr. Pike pointed out that an airplane can linger in one place, continuously watching for signs of activity that might be missed in a static picture taken by a satellite.