The Georgetown waterfront from the Potomac River to the C&O Canal - an area of the city that has hundreds of millions of dollars of development either under way or planned - would be preserved as a national park under a controversial bill just introduced in the Senate by Sen. Charles McC. Mathias Jr. (R-Md.).

Under the bill, the federal government could take by eminent domain Georgetown property between the canal and the river, and between Rock Creek and a line 400 feet west of Key Bridge, at the March 1 fair market value of the property.

Mathias said in a statement that with the introduction of his bill, "Developers will proceed at their peril, since property on the Georgetown waterfront can be acquired at its current market value rather than its value after buildings have been erected."

The historic Georgetown waterfront, a bustling tobacco and grain port in the 18th century, has been the site of controversy for years. Last November, D.C. Superior Court Judge Sylvia Bacon upheld a rezoning of the waterfront, paving the way for condominiums, hotels, apartments, restaurants, specialty shops, a boat dock, tennis courts, offices and stores in the area between M Street NW, the Potomac River, 28th Street NW, and Key Bridge. The judge's ruling was praised by developers but harshly criticized by citizen associations, and an appeal now is pending before the D.C. Court of Appeals.

"The Georgetown waterfront is now threatened with massive high rise development which would impede the vistas to and from the Potomac and would be out of scale with the historic neighborhood. . . . If historic preservation has any meaning, it should be assisted in our nation's capital." Mathias said in a statement introduced into the Congressional Record.

But developers with multimillion-dollar projects either under way or planned for the area affected by Mathias's bill expressed shock at the measure.

Bruce Lyons, spokesman for a development company which plans a complex of town houses, apartment condominiums, offices and shops on the site of the older paper mill, yesterday said he had not yet seen a copy of the Mathias bill, but from information he had received about it, found it "incomprehensible." He said his company already has poured $11 million into the project.

"I don't understand what he's suggesting," Lyons said of Mathias. "It makes perfectly good sense to make the waterfront from K Street to the river a park because that's workable, but buying everything south of the canal is talking about a billion dollars. Do you think the federal government is going to authorize a billion dollars?"

Lyons said that at this point, he does not feel threatened by the bill. "It still hasn't passed. I don't think they have the constitutional right to do that. It's unprecedented. The Supreme Court will have to rule on a seizure of this type."

Robert Morrison, who plans to put a late 18th Century-style inn and offices, condominium apartments and a town house, south of the canal, called the bill "beyond my comprehension." He predicted that the District government will fight it "tooth and nail."

Georgetown residents and civic groups who have fought the proposed large-scale development of their community for years praised the bill.

"Sen. Mathias's bill is like a life preserver to a drowning man," said Sara Blunt, vice chairman of the Georgetown ANC. "I am sure that the residents here and all along the Wisconsin Avenue corridor who have been frustrated for so many years in their negotiations with the city's planners and the zoning commission will support this measure."

The ANC, informed of Mathias's plans before the bill's introduction, held an emergency meeting Feb. 20 and supported the measure, asking that the waterfront area be protected from development inconsistent with the "scale, texture and historic nature" of the canal and Georgetown.

The resolution asked that private houses be exempted from the legislation, but Mathias left such a matter up to discretion of the secretary of the interior in his bill.

Olcott Deming, president of the Georgetown Citizens Association, said he is "pleased, delighted" about Mathias's bill. He said he is optimistic about passage of the legislation.

Deming said he has no idea how much acquisition of the property would cost, "but spending in the two-digit millions would seem prudent to acquire land on the doorstep of the capital of the United States. . . . It's in the Georgetown interest, the capital interest and the national interest."

Under the rezoning upheld by Judge Sylvia Bacon, most of the development of the area included in the bill is limited to 40 feet and 60 feet in height, with a small area south of the canal between 31st and 29th Streets NW possible for 90 feet high buildings, according to J. Kirkwood White of the D.C. Municipal Planning Office. White estimated that it could cost the federal government from $100 million to $200 million dollars to acquire the land and buildings between the canal and the river.

A spokesman for the Georgetown Inland Corp., which owns a large portion of the waterfront property, could not be reached for comment.

Ben Gilbert, director of the D.C. Municipal Planning Office, noted that much of the land between K Street NW and the river is owned by the District government, and he said he approves of the idea of a park for that smaller area.But he added, "before we surrender it (the property), we have to determine what's going to be done with the Whitehurst Freeway. We need to evaluate our needs."

Gilbert also said he felt that extend in the park all the way north to the canal "is unrealistic in terms of cost . . . None of our plans have contemplated that kind of thing."

Arthur Cotton Moore, an architect who has been involved with the design of many buildings near the Georgetown waterfront, said yesterday that the legislation probably will please "both the antidevelopment people and the large landowners. Who will lose? The people, in terms of taxes and revenue. The big issue is that we will lose in terms of our onlu opportunity in Washington to have a European-style waterfront, our only remaining hope for a civilized urban use of the waterfront."

Moore said the bill "creates a cloud - a nonpurchase cloud - over the area. It's an attempt tostop development." He added that he does not believe Congress will pass the legislation. "There's no way they will come up with hundreds of millions of dollars."

Jack Eddinger, press relations director for Sen. Mathias, said thsenator's bill is similar to one Sen. Edward Kennedy (D-Mass.) introduced several years ago which safeguards Nantucket Island.

"The senator has been interested in the issua for a long period of time, "Eddinger said. He said Mathias had met with Georgetown civic association leaders for the past month discussing the issue. He said that senator had not met with developers in the area.

Charles Atherton, secretary of the Commission of Fine Arts, noted that the commission has recommended to the Department of the Interior that a smaller area of the Georgetown waterfront, south of K Street between Key Bridge and Rocky Creek Park, become part of the National Park System.

"We're interested in furthering any extension of the park system on the Georgetown waterfront, but whether it should extend all the way up to the canal is another matter," Atherston said. "Construction will make it very difficult and very expensive," since most of the property north of K Street is in private ownership.

Atherton added, however. "We ought to really sit down and think about it."