My Coney Island beacon. The last civilian lighthouse keeper talks about leaving his special island home of 28 `light-years'

FRANK SCHUBERT became a lighthouse keeper more than half a century ago for reasons more practical than romantic. When Mr. Schubert first signed on with the US Bureau of Lighthouses, a branch of the Department of Commerce, in 1937, ``jobs were scarce.''

Two years later - just when he was promoted from buoy tender to lighthouse keeper - Franklin Roosevelt shifted responsibility for the nation's lighthouses to the Coast Guard.

And today, Schubert, a craggy-faced man of 72 years, is the last civilian lighthouse keeper in the United States, according to the Coast Guard.

In October 1989, when the country's 12 remaining manned lighthouses will become fully automated, Schubert will retire. He is ambivalent about the passing of an era that has seen civilian lighthouse keepers gradually replaced by men in uniform - who in turn are being replaced by machines.

``It's kind of rough,'' he reflects, ``but I don't feel so bad about it.''

Schubert's taciturn manner belies an intense pride. It surfaces when he shows off the Coney Island Light Station, his home and workplace since 1960.

The lighthouse rises 75 feet above Norton's Point on the southwestern tip of Brooklyn. Its white, cylindrical tower is supported by a skeletal frame of wrought iron and steel topped by a black watch room and light chamber. The tower was built in 1890, and it shows little evidence of nearly a century's worth of wind, fog, and salty sea air.

Every day at dusk, Schubert clambers up the tower's winding stairs and climbs an eight-rung ladder to the light chamber.

As the sun drops behind Staten Island, he checks the six-sided lamp of nine cut-glass prisms surrounding a bull's-eye lens. This great glass globe, built in Paris in 1897, is framed by brass casings floating in a pool of mercury.

When satisfied that all is in working order, Schubert throws a switch that lights a two-inch-long 1,000-watt bulb. The concentric glass prisms reflect the light into a single, concentrated beam that sweeps seaward toward the horizon. The beacon flashes every five seconds and can be seen by ships as far as 14 miles away.

Schubert says that life as a beacon keeper is a lot easier now than it was when he began work at his first lighthouse, on Orchard Island, a tiny spit of rock three miles off Staten Island.

He no longer has to collect rainwater for drinking and showering, or wind cables to make the beacon revolve. Nor does he have to share cramped quarters with two other men for 21 days at a stretch.

But the lighthouse still demands constant attention. According to regulations, the station can never be left unoccupied. Schubert, who lives in a seven-room cottage next to the lighthouse, hasn't taken a vacation in 27 years.

And when a power failure blackens the beacon (``It always seems to happen at 3 a.m.''), Schubert has to quickly set up an old kerosene lamp inside the revolving lens. He is the lighthouse's custodian, painter, carpenter, and electrician.

``The Coast Guard sees lighthouse keeping as an assignment, and the lighthouse as a station,'' he mused.

``But for me, this is home, and I've taken good care of it.''

After a 19-year hitch tending three lighthouses on Governors Island, Schubert arrived at the Coney Island Light Station with his wife, Marie, who died two years ago, and his daughter and two sons.

That first year Thomas and Kenneth Schubert, then 13 and 10, joined the Sea Cadets to learn boating. They caught fluke and striped bass off their own rocks. One morning they came out to find an 18-foot whale stranded on the beach. Marie became Frank's unofficial assistant, ready to take command in an emergency.

The Schubert clan has grown to include seven grandchildren. Holidays are an excuse for large family gatherings on Norton's Point.

``It's a much better life than I have any right to ask for,'' Schubert remarks as he looks toward a horizon dotted with harbor islands and ships plying the Atlantic.

During his 28-year tenancy, Schubert has seen 80 feet of his backyard devoured by the sea. The brick-and-stucco houses of Sea Gate, a private community, now cover the acres of meadowland that once surrounded the lighthouse.

Because of newly installed, delicate radio equipment, Schubert can no longer take Boy Scout troops or high school science classes inside the lighthouse.

But he welcomes the weekly round of visitors who appear at his gate. In this age of automation, he recognizes the city dweller's need to get a glimpse of a resident lighthouse keeper's way of life - before it vanishes.

``People around here, they hear so much about lighthouses, but they have so little chance of seeing one,'' he says. ``Sure they can come out. They don't bother me.''