LONDON -- Radical change to the design of roll-on roll-off ferries like the Estonia could be made compulsory within two years, the head of the International Maritime Organization said Tuesday.


William O'Neil, secretary general of the IMO, ordered a safety review after the ferry Estonia sank in the Baltic Sea in late September, killing 910 people.


"Safety is paramount," O'Neil said in an interview.


He said a panel of experts would be set up at a December session of the Maritime Safety Committee of the IMO, a UN agency that polices safety at sea. It would make recommendations by next May which could be translated into international regulations by early 1997.


O'Neil said the panel would have a broad brief including ways to deal with the basic issue of water control on a ferry vehicle deck. A relatively small amount of water sloshing about on ferries' vast decks can cause the vessels to capsize.


He said the panel would look at the question of introducing bulkheads or dividing walls on the car deck to control water that entered the ferry, whether through accident or operational mishap -- as happened when the Herald of Free Enterprise sank in 1987, killing 193, when a bow door was left open.


Some shipping firms have said bulkheads would prove too costly, using up car space and slowing down turn-around time.


But O'Neil said he felt that ferry companies would take safety as well as commercial considerations into account. "I don't think that where reasonable suggestions are made by the panel the commercial world would not go for them," he said.


Up to now, the ferry safety question has centered on preventing water getting on to the vehicle deck.


O'Neil said that studies had already been carried out into various collapsible and folding bulkheads, and the issue was whether they should be fitted, not their basic design.