Four different plans for redeveloping key portions of Alexandria's decaying waterfront at virtually no cost to the taxpayers were presented last night to the City Council.

The plans call for public walkways and parks, town houses, restaurants, shops, a seaside plaza and docking for ships. All involve restructuring the city's mammoth Torpedo Plant complex - four old factory buildings that occupy some of the most valuable real estate in the Washington area.

The City Council will select a developer for the complex and could reject all four of the plans submitted last night.

The developer chosen for the project must buy some of the property, from the city, work out lease arrangements for the use of other parts and pay for the realization of the development proposal, including demolition and construction.

Development costs are expected to run between $12 million and $24 million, and the estimated $300,000 in tax revenue the project is expected to generate would compensate the city for increased police, fire and other serivces.

The four hulking gray buildings are clustered at the Potomac River north of King Street, one of the main shopping axis in the city's Old Town area. Built by the Navy in World Wars I and II, some of the buildings housed torpedo manufacture operations and have walls six feet thick meant to withstand accidental explosions.

For years the buildings were used by the U.S. government as a repository for World War II military records. The buildings were sold to the city several years ago.

Although a popular Art, Center, with studio and gallery space for a variety of artists, occupies much of one of the buildings, the others have broken windows and boarded up doors that contrast with nearby shops, restaurants and $125,000 town houses.

The city required that the redevelopment proposals provide 70,000 square feet of space to retain the Art Center.

All the proposal call for eliminating at least a quarter of the Torpedo Plant structures, which occupy 6.25 acres and have 380,000 feet of floor space.

Demolition would create several hundred parking spaces required by the city, according to City Manager Douglas Harman.

A $22 million proposal by the Redstone Development Corp. calls for eliminating the upper two stories of two of the four buildings and creating 150 town houses wihtin the largest of the structures, located opposite historic Carlyle House on Lee Street.

That redeveloped structure, which currently houses a ground-floor garage, also would contain a public plaza.

The proposal by the Lenkin Co. would place an archway across lower King Street, open up the building that currently houses the Art Center into a public courtyard, and taper back the roofs of several buildings in order to achieve the desired reduction in total volume. Colonial style facades also would be added to around several buildings, and tennis courts would be placed near the waterfront.

The plan by the Alexandria Waterfront Restoration Co. would lower the front of the large parking building facing the Carlyle House so that visitors to it would be able to see the water's edge for the first time in decades. A waterfront plaza featuring dozens of boat slips and a floating restaurant in a tall-masted, achored ship also would be created.

The plan by OTV/Watergate Developments Inc. calls for demolishing the northernmost of the four buildings and turning the land into a park-plaza area. The plan also would create man-made islands in the middle of the harbor area.