In the frigid expanse of Antarctica, an enormous iceberg sheared off from one of the world's largest ice shelves and began a meandering four-year odyssey at sea, ultimately lumbering into the shipping lanes off the tip of South America early last month.

The iceberg itself poses little immediate danger. Accidentally running into it would be like accidentally running into Rhode Island. More troubling are the smaller icebergs, some as big as a football field, that tend to break off the larger berg and become silent floating menaces.

Thousands of miles away in a rundown, Eisenhower-era office building in Suitland, federal scientists at the National Ice Center huddle around large computer screens tracking the latest satellite images of the monster berg--known as B-10A--and its offspring.

Tracking these huge slabs of ice, and occasionally issuing public warnings about them, is only a tiny piece of the work that goes on each day at the ice center, one of the more obscure outposts of the federal bureaucracy.

The larger mission of this odd assemblage of civilian and military meteorologists and geographers is to map the world's sea ice--most of it decidedly stationary--and post their findings each week online (at www.natice.noaa.gov on the World Wide Web) for anyone with a modem, and an interest in the cold stuff, to peruse.

The center--funded mostly by the Navy and the National Oceanic and Atmospheric Administration and partly by the Coast Guard--gets most of its attention for the work it does with icebergs. But Cheryl Bertoia, director of ice operations and a geographer by training, wants to be very clear: There is a whole lot more than iceberg-gazing going on.

"We've hit the news quite a few times recently with icebergs. But we don't really do icebergs. We do sea ice," Bertoia said in an interview at her office in Federal Building No. 4 in the Suitland Federal Center on the outskirts of Washington.

Each day the center receives data on sea ice from polar-orbiting satellites--American and foreign--floating buoys, meteorological models, aerial ice reconnaissance (actual human beings peering out airplane windows), and ship and shore station reports.

Analysts then sift through the data to produce the most accurate possible images of the location and quality of ice formations in any given region.

The images are then posted on the Web and delivered in software packages designed for Navy and Coast Guard ships, particularly icebreakers. The images are also used--at no cost--by foreign governments, the scientific community and commercial ships that may need to navigate icy waters, especially larger ships unable to use the Panama Canal to bypass South America on the way to the Pacific Ocean.

All the images are created in the ice center's operations room, which lies behind a secured door accessible only with a magnetic pass.

A handful of ice analysts hover over their computers, assembling the incoming data. Analyst Mary Keller is mapping the Barents Sea, which lies in the Arctic above Norway and Russia and "melted out" more than a month ago.

Keller doesn't get really excited, however, until she boots up another computer with the latest images of B-10A, immediately betraying the nonchalance with which Bertoia and others at the center treat icebergs.

B-10A is headed toward the tip of Argentina. But if it fails to break free of the circum-continental current that swirls around Antarctica, it could ultimately reattach itself to the ice shelf. If it does keep heading north, it will continue to melt away, like Frosty the Snowman, in the warmer waters off the South American coast.

But while B-10A is unlikely to crash into Argentina, it is the melting process that creates smaller icebergs with the potential to wreak Titanic-style havoc on unsuspecting ships in the area.

"These are all tiny bergs right in here," said Keller, pointing to minuscule shadows on the radar image of B-10A. "And ships would miss these because they are right down at the water level, and right now the light is very low down there because they are just starting to come out of the Antarctic winter."

These smaller bergs can appear out of nowhere, particularly during heavy Antarctic storms when a ship might easily miss them because its radar only picks up images of rippling waves crashing in the darkness.

Forget B-10A, which is wider than the District of Columbia and longer than the stretch of I-95 from here to Baltimore. "I don't think anybody is going to hit that. But these," Bertoia said, pointing to the smaller bergs, "these are a real problem."

CAPTION: Cheryl Bertoia, director of ice operations, maps the progress of bergs such as B-10A, which is heading for Argentina.