THE vessel Vito C is docked here at the Gloucester port, ``icing up'' for another week-long fishing voyage in the Atlantic. Crew members are busy tying lines, stacking crates, and replacing deck tiles damaged by a chemical that burst from a 55-gallon drum the crew accidentally hauled up in a fishing net two weeks ago.

``The barrel started spraying like an aerosol can when she hit the deck,'' recalls Capt. Frank Ciaramitaro, waving his hands in the air. ``The smell was so strong we choked, and our eyes watered. We didn't know what we were inhaling. It made us dizzy.... I've never seen anything like it before.''

The crew immediately called the Coast Guard, threw the barrel overboard, and washed themselves and the boat. They also took a small sample of the chemical. Later, tests by the Environmental Protection Agency (EPA) determined the substance to be carbon disulfide, a hazardous byproduct of industrial and biological processes.

``Whatever it was, it was eating up the fish,'' Captain Ciaramitaro says, displaying a photograph he had taken of a fish that got sprayed by the chemical; its scales were burned dark gray.

Hauling up barrels of toxic waste in fishing nets that scrape the ocean floor is not an uncommon experience in Massachusetts Bay. Last year, a Gloucester fisherman hauled up a barrel which burst. He has not recovered from the effects of the incident and has lost his boat and his livelihood.

Most local navigators know to avoid the ``foul area'' 10 miles off the Gloucester shore. On Ciaramitaro's chart it is labeled ``Avoid: Explosives.'' Barrels of low-level radioactive waste and toxic chemicals were legally dumped there from the World War II period into the mid 1970s.

But encountering a barrel of unknown origin and contents 120 miles from shore is a new wrinkle in the existing problem of what to do with the former dump site, and with the question of how far the problem reaches.

Environmentalists are seeking answers about the condition of the barrels and what, if anything, should be done about them. Are they leaking and contaminating the ocean-bottom sediments? Should they be covered up or removed from the ocean? Are they leaking, contaminating sediment and marine life?

And is the toxic trash traveling to other areas, or was Ciaramitaro's shocking catch simply a fluke some 100 miles from the site, in the rich, pristine waters of Georges Bank?

The questions are not limited to the Northeast. San Francisco's ecologically diverse Farallon Islands area contains some 47,500 barrels of radioactive waste lying 3,000 to 6,000 feet deep on the Pacific floor, 30 miles from shore.

``A high proportion of barrels have damage from implosion [being crushed by water pressure]. Some are broken and the contents are leaking onto the sea floor,'' says Tom Suchanek, a research ecologist at University of California at Davis. He says EPA tests from 1974 showed radioactive sediment levels 1,000 times above normal. ``What that means in terms of potential health risks to humans or ecological systems, we just don't know,'' says Mr. Suchanek.

What scientists do know is that the barrels have reached the limits of their ``life expectancy'' for containment. Saltwater erosion threatens to result in their leaking or bursting. Tidal action and fishing nets are scattering the barrels around. Some drums containing radioactive chemicals (like plutonium and cesium) in the Atlantic and Pacific sites are lined with concrete; many are not.

In the Northeast, an EPA study in 1980-81 found no danger of radioactive waste in sediment surrounding the ``foul ground.'' But contamination by toxics was not tested, and environmentalists want more studies.

``My hunch is that there's a bigger problem from the toxic chemicals than there is in radioactive waste,'' says Eleanor Dorsey, a staff scientist at the Conservation Law Foundation, an advocacy group based in Boston. In addition to more tests of marine life and sediment in the area, the foundation wants the EPA to figure out whether the area should be covered up with clean dredge material or removed.

Covering the area seems to be the better option, says Ms. Dorsey, because removal presents too many dangers. Pulling the barrels up to the surface might cause them to burst, dispersing their contents. Because no records exist identifying the contents, every barrel would have to be opened and tested. The process would be hazardous to people who handle the barrels, she says, concluding: ``I wouldn't be surprised if we'd be better off leaving them there.''

The situation is more difficult in California, because the barrels are so deep, says UC Davis's Suchanek. ``The sediment would just disperse. It wouldn't go to the bottom and cover them.'' Yet while the federal government has agreed to fund a $900,000 study (by the National Oceanographic and Atmospheric Administration) in California's foul area, New England's problem appears to be hampered by a lack of funds. ``This year we're going to try to do some work to locate the barrels, and to determine their position,'' says Gwen Ruta, chief of marine and estuarine protection at the regional EPA office in Boston. ``But only as funds allow.''

Aboard the Vito C, Captain Ciaramitaro is wary. He estimates that he lost $5,000 to hospital costs, boat cleanup, and wasted time after that last haul. ``We're going back out to the same place, because there are a lot of fish there. I just hope we don't pull up another barrel like that last one.''