WASHINGTON'S CREEPIEST hotel--where the bats, rats, birds and other roomers without credit cards can congregate nightly in the lobby, undisturbed by anything other than an occasional false alarm report of a renovation--is the Willard, which has been rotting on its famous corner for 13 years now. But the Willard is also a landmark with history galore on every floor, which is why so many people have tried so hard to bring it back alive. Now there are reports that Washington developer Oliver T. Carr has succeeded in gaining control of the current rescue mission--and that is the most encouraging news yet.

Yes, we can all hear the yelps of those who have been portraying Mr. Carr as a coldhearted killer of historic buildings, merely because he has not seen fit to incorporate the old Rhodes Tavern in a project along with other, more attractive facades that he has agreed to preserve. But more than a few of the organizations dedicated to historic preservation agreed with this trade-off and have found Mr. Carr something less than the villain described by the tavernites of the don't-even-move-Rhodes-to-another-site school.

If there is cause for optimism--and that itself is appealing after all the setbacks--it lies in Mr. Carr's record for getting things done. Until now, and for many reasons beyond their control, previous developers of Willard restoration schemes have just not been able to come up with the money. Score one for Mr. Carr, at least, because he has pledged financing; in return, he is to get a major say in revising the plans for the hotel and for adjoining commercial property.

Under the proposal now being worked out with Florida developer Stuart S. Golding, who had exclusive rights but not the financing, the old Willard will be made into a luxury hotel with shops and with a new office building next door. The exterior of the office building apparently will mirror the Willard's grand old facade--which is critical to any renovation plan. Mr. Carr has insisted from the beginning that the hotel project couldn't pay for itself without additional commercial office space.

Ideally, the complex should include some less- than-luxury housing, too, and that possibility should be addressed by Mr. Carr before any agreements are sunk into concrete. But meanwhile, that wallpaper and plaster keeps falling into the pools of water on the lobby floor; and, from top to bottom, the old building surely is weakening by the year. The Willard is Washington's most prominent disgrace of local and national significance--and that is a compelling reason for giving the latest effort to revive the hotel all the constructive support the city and the administration can deliver.