Representatives of several citizen and environmental groups last night criticized a proposal by a private developer to fill in part of the Potomac River to construct a floating dock and a 700-foot public boardwalk as part of a Georgetown waterfront project.

The latest dispute in the long-running controversy over the prized waterfront property focuses on an attempt by the developer to get permission for the shoreline work from the Army Corps of Engineers and the National Park Service. Officials of both federal agencies held a public hearing on the developers' request last night, but a decision is not expected for months.

As part of the $154 million residential and commercial project, between 30th and 31st streets NW, the developers want to build a sea wall that would require them to dredge and fill along the 700-foot stretch of the Potomac that borders their property.

In addition, they want to construct a floating boat dock out into the river, and dredge a channel that would lead to a boat basin in the center of the project. The development is planned by Western Development Corp. of Georgetown and CSX Resources Inc. of Richmond.

Spokesmen for rowing clubs and high school and college rowing crews added a new twist last night when they argued that the floating dock would cause hazardous conditions by attracting more motor boats to the area, now a prime rowing spot.

A spokesman for the developer said the proposed dock and other improvements would not endanger rowing in the area, and offered to work with the rowing clubs to ensure that power boats do not interfere with their activities. "Most urban rivers like the Charles River in the Boston area have both," said Arthur Cotton Moore, architect for the project.

Moore disputed other contentions by opponents that the project was unsafe and carries a risk of severe damage by a flood. He said that the plan to replace the existing "jagged" sea wall will eliminate "a very dangerous" condition. He said the proposed boardwalk would be secure from flooding and would provide public access along the waterfront. The floating wharf also would be open to the public.

Moore added that he believes opponents were using the sea wall work as an excuse to continue their efforts to block the entire project, which is being developed on six acres and will include offices, shops and custom-built homes costing up to $500,000.

Citizens groups opposed to commercial development along the waterfront unsuccessfully sought to have the site converted into a waterfront park. But their efforts failed when the D.C. Court of Appeals refused last fall to overturn the city's approval of the development.