The U.S. Senate yesterday moved for the first time into the protracted struggle over Georgetown's waterfront, passing a bill intended to preserve the land from development.

Developers of the tract immediately said they have no intention of going along with the proposal, which requires their agreement.

The bill, sponsored by Sen. Mark O. Hatfield (R-Ore.), a Georgetown resident, would allow the Interior Department to swap a tract of federal land for the 3.5 acre Potomac River shoreline tract now being turned into a residential and commercial project.

The bill, which must also pass the House of Representatives, does not require the department to offer the land exchange, nor does it require the developer to accept.

Still, the bill's passage was cheered by a spokesman for the Georgetown group that wants the tract turned into a park, even as it was being dismissed by officials of CSX Resources, which is developing the controversial $154-million project with the Washington-based Western Development Corp.

"It's just great," said Donald Shannon, president of the Citizens' Association of Georgetown. "I hope CSX will see the great benefit they could confer on the nation's capital if they would take advantage of this legislative opportunity."

But Herbert S. Miller, president of Western, said through a spokesman, "I would like to make it unequivocally clear that we and our partners will not undertake the voluntary transfer of the Georgetown site. We have already invested more than $25 million for land acquisition and architectural and design fees, and construction has begun."

The tract is part of a much-disputed area between K Street and the river that became the subject of a 1979 agreement among the D.C. government, the Interior Department and the private developers. Under that agreement, the city would donate its 12 acres to the department for use as a waterfront park. The developers would donate about 3 acres of adjoining land to the park and the remaining 3.5 acres would be privately developed, with any plan requiring approval of the city government.

Despite the agreement, the citizens' association has continued to dispute the development and last year asked the D.C. Court of Appeals to overturn approval of the project by the city's historic preservation officer. Though that case is pending, the city last spring issued building permits for the project, and according to CSX spokesman Ed Adel, "The day after the permit was issued, dirt was moving."

Western plans to build four new buildings containing condominiums, offices and shops.

Told of the Hatfield proposal to swap the 3.5 acres, with its views of Washington and the Potomac, for an unspecified federal property of equal value, Adel chuckled and asked, "Where? With a view of the Kennedy Center?"

He also noted that the bill is "discretionary."

Shannon, however, said that despite its discretionary nature, the bill sponsored by a powerful committee chairman like Hatfield should have some impact. "Let's put it this way. I think the Senate Appropriations chairman carries a great deal of weight with any member of the administration."

A spokesman for Interior said, "There's nothing really in the works as to a plan to exchange property. The bill's got a long way to go. We would look into the situation at the time a final bill is passed by the House ."

The Congressional Budget Office reported that the 3.5 acres has been valued at between $12 and $40 million by various sources.

The dispute over use of the land has run for years, and last spring critics accused Mayor Marion Barry of breaking a 1978 campaign promise to oppose commercial development of the waterfront. Barry had promised the citizens' association that he would support their efforts for a park, but after he was elected, members of his administration came out in favor of development at the site.

Barry asserted at a meeting last April that he still favors a park, but is bound by law to abide by decisions that the site may be developed as long as the construction is compatible with existing use of adjacent property.

Yesterday, James O. Gibson, assistant city administrator for planning and development, said through Barry's spokeswoman Annette Samuels, "The city's waterfront land in Georgetown is still committed to become a park. The Senate's action reaffirms Sen. Hatfield's longheld commitment that negotiations ought to occur between the developer and the Department of Interior."

Asked whether that meant the Barry administration supports the plan, Samuels said, "It doesn't mean we do or don't support it. And that's the way we want it."