The heyday of Alexandria as a seaport may be long gone, but come spring, things are expected to boom on the city's rejuvenated waterfront. The city will open a $2.5 million, 51-boat marina April 15 that is expected to spur more revenue and sales taxes for the city.

Besides boat slips for small vessels up to 40 feet in length and a number of berthing areas for larger charter boats, cruise and special character vessels, the marina area will have a restaurant, shops, an arcade, a market, trails for pedestrians and bikers, and shower and restroom facilities.

It has been "100 years since it the waterfront was a booming point," said Mayor James P. Moran, who envisions the marina as a "very attractive, urban center of activity" like "Harborplace but on a much lower scale." The marina will "give us the kind of use of the waterfront that will enhance the downtown . . . ," said Moran. "People will pull their sailboats in . . . , go to restaurants, sit, dine and look at the water."

The staffs of the planning and recreation departments have estimated that operating the marina will cost about $46,000 annually and should be offset by $32,000 to $65,000 in revenue. In subsequent years, revenue should increase at a greater rate than operating expenditures, city officials say.

Business owners are looking forward to the marina's proposed April 15 opening. Paul H. Bynum, manager of the Sea Port Inn located at 6 King St., said he hopes the marina will "promote business, with people coming in on their boats."

Residents also await its opening but raise one major concern -- parking. Dr. Simon Russi, who lives across from Founders Park, said he has "no particular objections to the marina," but he said it "may cause parking problems."

According to Joseph Hensley, director of the Department of Recreation, Parks and Cultural Activities, the marina's opening will not add significantly to the city's parking problem. "The residents knew that the marina was going to open. This is nothing new."

Discussions with local businesss, community and boating groups will be scheduled before a Feb. 22 public hearing to work out the details of the marina and the location of an official Alexandria dockmaster post on the waterfront.

The marina will have four piers to provide access to the boats. The renovation of the Torpedo Factory north pier and south pier was completed in the spring of 1985. This month, construction of the new Founders Park north pier and south pier will be completed and dredging of the hydrilla and deepening of the water level under all the piers also is expected to get under way.

Most commercial vessel docking will occur at the Torpedo Factory north pier and the Founders Park north pier. Transient vessels wishing to dock at a city pier for several hours or the day will be directed to the slips at the Founders Park piers.

There will be no provisions for houseboats or lease space and the bulkhead at Waterfront Park will be used for overflow docking. Transient vessels wishing to dock at a city pier overnight will be directed to the slips at the Torpedo Factory south pier, where water and electricity will be made available.