IN THE MIDST of last week's Super Bowl euphoria, Redskins owner Jack Kent Cooke delivered an ultimatum to the District of Columbia. He said during an interview with WJLA-TV that the city has until June 30 "to come up with a solid proposal" for a new domed stadium seating some 75,000 people. "Failing that," he said, "it's going to be necessary for us to go to one of the surrounding counties and say, 'We've exhausted every means of keeping the stadium in D.C. . . . we are now awaiting bids from each of the counties to determine which is the best one for us to move to.' " This week a group of private investors said it is prepared to build a grand complex in Loudoun County consisting of a hotel, a shopping mall, condominium homes and a Jack Kent Cooke Presidential Stadium.

If all this sounds like a call to action, it is: it's a clarion call to the city of Washington to think small and sit tight. Think Wrigley Field, Fenway Park, Boston Garden and all the other antiquated, beloved arenas that people continue to enjoy because their cities have not been stampeded into gigantic public works projects that they can't afford and don't need. Sit tight in RFK, an open-sky, grass-bottom oval in the monumental heart of Washington and the repository of more than a quarter-century of Washington sporting tradition.

In the event that the private developers could assemble the land and the financing for their project and get it all approved by Loudoun County, there probably would be little the city could do to keep the team in town. Mr. Cooke says the Redskins can't make money in 55,000-seat RFK. Not even if they raised ticket prices which, at an average of $20 a game, are far below what the market will bear? He'd like a domed stadium so the Super Bowl could be played here. When? Every 10 or 15 years? And does Washington really need the Super Bowl to put it on the map?

RFK Stadium is still a good place to watch a game, and will be for many years to come. Perhaps it should be fitted with private "skyboxes," which the Redskins could resell or rent to those who can afford them. Certainly the city should offer a better lease arrangement to the team and do all it can to deal with fans' complaints, whether they concern maintenance of parking lots, long lines at vending stations or plumbing breakdowns in the restrooms.

But one thing the city has no business doing is getting financially involved in a project that could cost hundreds of millions of dollars and has little likelihood of ever paying for itself. So far the District and its surrounding counties have avoided entering into a bidding war for the Redskins. This is an indication not only of the good relations that exist among them but of their mutual realization of this truth: that tax money doesn't come easily, and revenues collected from the people should be used wisely and prudently -- to pay the teachers, house the homeless, pave the potholes and do the thousand other things that governments need to do before they start financing indoor football.