DON WE NOW OUR hip boots and foul- weather gear for another depressing trip into leaky old Union Station, long the unproud home of not much at all except downpours of water and federal dollars and, it is said, a flourishing rat population. It is here that an ingenious alliance of miscalculating bureaucrats from various White Houses and Congresses managed to convert a proud and wonderful train terminal into a national sinkhole without rival. In fact, today -- in what was ripped up, remodeled and ruined in the disguise of a "National Visitors Center" -- you can still see the symbolic sinkhole in the floor, an enormous divot where even in this ersatz center's heyday nothing ever came to pass except a slide show.

We return to the subject because it doesn't go away--and it's costing everybody $3.5 million a year just for a lease on the place. The only smart money now is on an effort to cut the losses by restoring the building as quickly as possible to its original, primary function as a lively and commercially successful transportation hub. That is why the forces of practical frugality, both in Congress and the White House, have recognized the necessity of committing money to the rescue mission.

Transportation Secretary Drew Lewis hasn't formally asked for funds, but he has told a congressional panel that his department is prepared to spend $70 million to bring trains and commercial life up front at Union Station, with office space upstairs and, eventually, a completed garage next to land that would be leased by the government to a private developer for conversion into more office/commercial uses.

But before we hear the thundering hooves of the boutiques-and-balconies contingent from the School of Awfully Advanced Urban Architecture, the site isn't exactly ripe for Harborplace II or Epcot North. What it can be is a pleasing complex where trains come and go and there are stores and restaurants and offices and whatever else might serve its Capitol Hill/congressional neighbors.

To do nothing is to waste federal money, which is why Mr. Lewis and members of the key committees in the House and Senate should work out a modest but serious proposal to cut the losses and end an expensive national embarrassment.