WERE THIS CITY not a good 2 1/2 years into modified "home rule" under an elected local government, you could easily conclude from the latest congressional arguments over the District of Columbia's budget that the not-so-good old days of colonial rule were still with us. At this writing, the House and Senate are deadlocked over the city's request for money to start work on a convention center. Moreover, if this impasse isn't resolved in less than a fortnight - when a just-granted continuing resolution will expire - the city will be without money for any purposes.

The city government, as you may know, goes through a ridiculously elaborate budget process each year, beginning with agency spending requests to the mayor that then travel in one form or another from the mayor to the city council and back and forth a few times before a budget is agreed to and transmitted to Congress for consideration there. That's also the route that the convention center budget request has already traveled - which means the center plan has the approval of the locally elected government, not to mention representatives of civic, business, labor and religious groups from all around the community. Yet Sen. Patrick J. Leahy (D-Vt.) wants to kill the money request because he thinks the city should look at other sites for the center and look into some private financing. The Senate, by a vote of 65 to 25, sided with Mr. Leahy.

But hold on. Now we find the dean of this city's congressional overseers, Rep. William H. Natcher (D-Ky.) stoutly defending the city's decision to move ahead with the convention center. As for the House position in conference with the Senate, Mr. Natcher is saying flatly that "we're not going to recede."

Now, no matter how residents may assess the merits of the convention center plan, anyone who supports the self-government spirit of the city charter should be willing to accept the fact that the matter has been studied, debated and decided by the local government, and should, accordingly, side with Mr. Natcher on this one. The House subcommittee chairman was correct on Monday when he characterized Sen. Leahy's rejection of the convention center as "a direct repudiation as far as home rule is concerned. . . . I don't think you should be in that position . . . regardless of how you feel about [the center]." Though we wish Mr. Natcher had remembered this argument when he cut money from the advisory neighborhood commissions' request and added money that the city didn't seek for police, we agree with him that Congress shouldn't be in the business of second-guessing the elected city government on important local matters.

Thus to hope that Mr. Natcher prevails on the convention center question is not necessarily to mebrace every last detail of the plan. As we have before, we will continue to raise questions about the center's development. But the way for those questions to be resolved is by the orderly precedures of self-government, downtown in city hall - not by an eleventh-hour power play on Capitol Hill.