IN SEEKING a $36.3 million supplement to the city's 1982 budget, Mayior Barry is asking for too much money and too little money at the same time. He is asking for too much money, for example, to begin a lottery and to set up a state constitutional convention. The lottery could be started with a short-term loan repayable from first-year profits without the city's putting up a dime. The constitutional convention, which District voters ordered last year, need not be accompained by a campaign to advertise the idea. Let the citizens themselves raise funds to advertise or to promote the idea of statehood.

On the other hand, there are some expenses the city must face now. The No. 1 threat to fiscal stability is the city's pension fund deficit. To keep that burden from growing every year, the District must put enough into the fund to pay the benefits due retired workers that year. But, despite indications that the city's bill for benefits next year will be over $140 million, Mayor Barry is asking for only $133 million. And his own financial advisers estimate he may be as much as $23 million short just this year.

The mayor also failed in this budget supplement request to ask for anything more than a 2 percent pay raise for city workers. He says that the city's new union bargaining procedure makes it presumptuous to set a higher mark without having negotiated the specific amount. We don't mean to be presumptious either, but where will the mayor get the money if the city's workers negotiate something more than 2 percent?

The answer may be that the mayor expects to raise taxes or to receive a higher federal payment. That next year is an election year makes a tax increase unlikely. To expect the federal government to pick up the cost, moreover, is to shirk the responsiiltiy to create a realistic -- a responsibility this city fought long and hard to win. Whatever happens to this request for a budget supplement, Mayor Barry appears to be asking for serious trouble for the city's finances with his current approach to budgeting.