Floods could periodically turn into an island the $100-million condominium, office and commerical complex proposed for the Georgetown waterfront, and its occupants could be forced to evacuate if the Potomac River overflows its banks -- which it has done frequently during the past decade.

But while the developer concedes flood waters might occasionally swirl around the project, the firm insists its planned earthworks, walls and drawbridge-like floodgates will make the complex a virtually waterproof castle.

They add that if last-minute evacuation became necessary, special rooftop stairs to the adjacent overhead Whitehurst Freeway would serve as gangplanks, permitting residents to escape.

The fact that the waterfront is on a flood plain is a major reason the federal Fine Arts Commission has voted against the project twice in the past six weeks.

However, District officials, ignoring the commissionhs advice, could issue building permits for the project -- although the city has already made such a move in the 70 years the commission has served as architectural arbiter for the Nation's Capital. But the project is particularly enticing to the deficit-ridden District -- the developer estimates it would provide 1,400 jobs and $8.6 million a year on taxes.

The developer, Georgetown Harbour Associates, has argued that construction on flood plains occurs all the time, citing the Watergate complex and the Kennedy Center. The firm's proposed flood-control measures are similar to those used in at least nine major developments around the country, including Baltimore's new waterfront World Trade Center.

The Georgetown plans call for installation of foodgates and berms, or earthen hills, that would rise 17.3 feet above the average low-tide level of the Potomac and would protect the project against all but the rarest and highest flood, said project manager John Pascale. Giant pumps would be installed to empty any water that did get into the project's ground-level shops and underground parking garages, he said.

District officials said last week they will recommend the project's evacuation whenever the Potomac reaches seven feet, which it has done at least three times in the past 10 years. At that level, the Potomac overflows onto the waterfront and triggers an evacuation alert for K Street property owners, says Sam Jordan, acting deputy director of the city's Office of yemergency Preparedness.

One reason the federal Fine Art's Commission opposed the project is a 1977 presidential order directing federal agencies not to approve developement on flood plains unless there is no practical alternative.

The Federal Emergency Management Agency also has urged that no major construction be undertaken on the flood-prone waterfront. Gary Johnson, acting assistant administrator for FEMA's flood plain management division, said last week the proposed development statistically has "a 26 percent chance of flooding at least once in 30 years" at a level of 17.2 feet or greater.

While the Georgetown waterfront has been inundated in at least 16 major floods since 1870, according to National Weather Service records, only three floods -- in 1889, 1936 and 1942 -- have reached or exceeded 17.3 feet.

The chief Weather Service hydrologist in Washington, Leo Harrison, said this week that flooding along the Potomac has worsened because increased development has meant there is less open ground to absorb heavy rains.

"We don't know if we've experienced the biggest flood stages yet.There could be floods several feet higher than any we've seen," Harrison said, particularly if a major rainstorm hits the entire upstream Potomac watershed. The 16 major Potomac floods in the past 110 years have been from storms that covered only part of the watershed, he said.

Pascale said this week that even if water were to go over or somehow get through the berms and flood-gates, there would be no danger to the buildings, and only ground-floor shops and offices and underground parking garages would be flooded. The project's built-in pumps would remove the water, he said. No residential units would be at ground level, he added.

Judith Bonderman, an Advisory Neighborhood Commission member and one of many Georgetown residents opposed to the project, says there is a nuisance factor as well as a safety factor when residential buildings are put in a flood plain and residents are asked to evacuate every few years.

"Somebody should call Hollywood. If this thing is approved by the city it's going to make a great set for a flood-disaster movie," Bonderman said.