DON'T LOOK quite yet, but Washington's ugliest natural resource--the Georgetown waterfront "blight-site" strip of rubble and ruin--at last may become useful and attractive: Mayor Barry has moved to build a city park that would complement Washington Harbour, the office/shop/housing and boat-basin complex that is set to replace some of the eyesores along this tract. While this won't satisfy the parkland-over-everything contingent in that area, nothing ever has, and it's high time the city moved ahead.

Preliminary plans calls for the park to be cleared and turned into grassy open space with trees and a promenade along the water. Coupled with all the nearby parkland along the canal, this should more than fill the bill for those in search of recreation space in Georgetown. But those in search of excuses for delaying action argue that Mr. Barry should let the National Park Service take over the land and make the park. That might be lovely, but there's a problem: the National Park Service has no plans to take on the job.

For the city to get going, Mayor Barry has asked for what amounts to less than 2 percent of the city's construction budget for the fiscal year that will start Oct. 1--and which is separate from the city's operating budget. That is hardly a bank-breaker; on the contrary, the sooner the job is done, the less expensive it is likely to be.

What has been fought over, delayed, redesigned, agreed to--and now put in motion--is a balanced use of a potentially attractive waterfront area that can yield new revenue as well as pleasure.