WHETHER WASHINGTON will have a civic center depends, still, on Sen. Patrick Leahy (D-Ct.), chairman of the Senate Appropriations subcommittee on the District. All he has to do is to approve the revised plan, which he ordered up last April and which city officials delivered in September. The House Appropriations subcommittee has already approved the revision; the Senate, in effect, has licensed Sen. Leahy to decided on its behalf. He has yet to respond.

In the revised plan, city officials met one of Sen. Leahy's earlier objections by making the center less costly. They met another by making it smaller in size. They followed his instructions to include financial involvement by the business community. They provided letters from a number of business indicating interest in building projects that could bring a substantial amount of new tax money to the city. In sum, city officials did exactly whast Sen. Leahy asked.

Or so it seems to us. But not to Sen. Leahy, who sometimes causes us to wonder whether there are any terms on which he would agree to end his long campaign against the convention center. His latest tactic is to question the good faith and financial soundness of business commitments made at his request and to his specifications.

For example, not too long ago we argued in this space that at least 11 of the 45 proposed projects were sufficiently promising to meet the senator's demands. He promptly challenged us to identify them. We are happy to oblige. Our list includes expansion of three hotels and construction of two more - including one right across the street from the center; renovation and expansion of the downtown Woodward and Lothrop store; construction of four office buildings as well as an office and apartment complex, and construction of 200 townhouse; near the center.

Now those projects may not be precisely the ones Sen. Leahy had in mind. But they would, we are persuaded, generate more than $10 million in new tax revenue for the city each year - clearly enough to meet the senator's requirement that new tax revenue cover the $7.5 million annual operating cost of the center. While Sen. Leahy may be somewhat dissatisfied with the terms of some of the other 34 letters of commitment that the city submitted, he should take considerable comfort in the thought that the proposal for a center has been substantially improved as a result of his persistence. Responsible enter prises are committed as firmly as they can be at this stage - in the absence of any firm commitment from Congress on a convention center - to produce some long-awaited and sorely needed new economic activity downtown, in conjunction with the proposed center. All that the senator needs to do now is give his approval to the project - declare a well-earned victory, if you will - and let the city get on with the job.