Intelligence scientists listening for covert nuclear blasts had their ears rattled by other explosive sounds -- the detonation of meteors as they streaked over the Pacific Ocean.

The Earth eavesdropping, conducted by researchers at the Los Alamos National Laboratory in New Mexico, was intended to detect atomic weapons tests by rogue nations or organizations in remote locations.

Instead, the Los Alamos listening stations picked up the sound of two large meteors as they plunged into the atmosphere off the coast of Mexico, the Los Alamos lab said this week.

The space rocks raced across the sky in April and August. But the lab waited to announce its findings until other U.S. space scientists last week confirmed the two objects.

The meteors were unusually big, between 6 and 10 feet in diameter. The first one created an explosive pressure wave with as much energy as 2,000 to 3,000 tons of TNT, according to Los Alamos researchers. The second, larger one could have produced a shock wave equivalent to 8,000 tons of TNT.

"Had anyone seen the April 23 event, they would have seen quite a show. That meteor was one of the five brightest ever recorded," Los Alamos scientist Doug ReVelle said.

Each year, listening stations at the lab record an average of 10 meteors 6 feet in diameter or greater. Those that appear as huge fireballs in the sky, like the April and August specimens, are known as bolides.

Bolides make dazzling displays dozens of miles above the planet. Fortunately, most explode into thousands of pieces or burn up entirely before they reach the surface. If these two survived, they probably smacked into the ocean, well away from populated regions, the scientists said.

The destructive capability of bolides that strike land is considerable. An extremely large one blasted the huge Meteor Crater in Arizona.

The unaided human ear cannot detect the low frequency pressure waves when at a great distance. But specialized microphones at four Los Alamos monitoring stations in the United States can both detect the infrasonic waves and help plot their locations.

The infrasonic information takes minutes or hours to reach the stations, which therefore cannot provide advance warning about approaching large meteors.

However, the Los Alamos scientists welcome the opportunity to monitor falling space rocks, which allows them to fine tune the instruments to use to detect nuclear blasts.