For the past century astronomers have waged an unequal battle against the mounting glare of electric lighting across night skies -- a smog of light pollution that renders faint galaxies all but invisible.

Two of the latest threats to astronomy stem from America's faltering economy and a widespread fear of crime.

One potential victim is the mighty 200-inch telescope on Mount Palomar, Calif., which has led the world in observational astronomy since the late 1940's. In 1984, San Diego, some 40 miles away, acceded to astronomers' pleas and replaced its white street lights with low-pressure sodium lamps. Astronomers love the pure yellow light because it is easily filtered from their instruments. But San Diego residents believe it aids thieves (though there is no proof of this).

The San Diego City Council, hoping to revive its downtown, is moving to replace its lighting with a lamp that could seriously degrade deep-space observations from Palomar.

Meanwhile, a Georgia company, Space Marketing, has announced plans to put a one-mile-wide reflective panel into space some time in 1996. Ostensibly a platform for scientific instruments, this satellite, which would appear nearly as large as the full moon, would carry a commercial message or symbol visible from the ground.

"The time may not be distant," said one anguished astronomer, "when we'll have to move to the far side of the moon if astronomy is to survive."