HIGH ON CAPITOL HILL for all to see is the Great National White Elephant, once a proud and bustling train terminal for Washington and points south, now a vast place where the trains are many long strides to the back, while up front is the largest open pit this side of Mount St. Helens. Its more formal name, which has pitifully little relationship whatever goes on there, is the Union Station-National Visitor Center. And its history is a monumental account of converging miscalculations and hideously expensive unfinished projects.

We recite this account of terminal illness not just to depress old-timers or brief the latest wave of spring tourists, but to point up the urgency of a bi-partisan salvage effort in Congress that could halt the expenditure of federal dollars that continues even as nothing is done at this site. If the whole structure were to collapse -- and it is crumbling at an alarming pace right low -- the federal government would still have to pay $3.5 million a year just for the lease it holds on the place. The longer the delay in doing something, the more expensive any solution will be.

That is why the key members of House and Senate committees, along with the Interior and Transportation departments, have worked out a trim and sensible proposal for undoing some past mistakes and converting this grand old building into a useful facility. If Congress fails to respond, the far more costly and wasteful alternative in the immediate offing is to shut down everything at the site for safety reasons.

By voting not to cut losses instead of sending more good money after bad, Congress can bring to this historically valuable structure 1) a station with conveniently located trains and 2) an efficient visitor center with attractive, rent-paying concessions of all kinds, including fine restaurants, boutiques and other services for tourists as well as commuters and townspeople, and 3) a modest garage for visitors' cars.

To rant in congressional debate about past waste is to argue for still more waste. The blame for this mess is everywhere -- from past administrations and Congresses to inflation, labor troubles, cost overruns, inadequate supervision, lawsuits, bankruptcies and transportation industry disputes. Now, Republican and Democratic leaders are supporting legislation to get the rescue effort going in earnest. There is a bill, H.R. 6674, ready to move through the House -- and its passage could not come a week too soon.