IT'S BEEN THE talk of Capitol Hill for years, but now everybody around town knows that the greatest source of leaks in Washington is Union Station. Today, this once-great port in a storm is a soaking mess, where the rain undrained falls mainly on the train. It is in desperate need of bailing out, and even though there's plenty of guilt to go around after years of bipartisan bungling and off-the-walls blue-prints, Congress has got to act, one way or another, right now; either fix it up or tear it down. Because it is a national teasure, and because Congress already authorized repairs and then didn't come through with the money, the only sensible solution is to put Union Station back together.

First things first: The roof has got to be repaired. Before the building was declared unsafe and closed down on Monday, heavy rains had poured through the roof, causing plaster to fall, ruining $5,000 worth of books and posters in the bookstore and slopping into two-inch-deep ponds on the filthy carpets that pass for flooring. Passingers who didn't choose to get drenched on a 400-foot outdoor detour to the tracks had to wade through the cavern where trains used to pull in until it was converted into a mausoleum, complete with an open pit suitable for the tomb of the unknown bureaucrat.

There are members in the House and Senate who recognize that to put off repairs or abandon the building is to approve of still more federal waste -- including $3.5 million a year that U.S. taxpayers are forking out just for the lease on the place. Sponsors of these rescue proposals don't pretend to excuse the series of compounded horris that produced this monumental abonination; as Rep. Sidney Yates (D-Ill.), chairman of the House Apporpriations subcommittee on interior and related agencies, has noted, "It doesn't make sense to me to be paying on an empty shell for the next 20 years. We've got to get a program."

And they had best not save it for a rainy day.