TALK ABOUT your expert testimony: John N. Mitchell, commenting in an interview with Credit Markets, a Wall Street investors' newspaper, has offered his own deep assessment of the District of Columbia government. Talking about the city's first sale of short-term bonds last month, Mr. Mitchell said, "I have never been in favor of the nation's capital issuing its own bonds. I certainly wouldn't be until they stop running the government like the Amos 'n' Andy Taxi Cab Co." And when John Mitchell talks about good government, he speaks with authority -- the authority of an ex-attorney general of the United States who capped his experiences with Justice in unique fashion. Who better to assess the management of this city's government than this disbarred bond lawyer who served time in a federal prison camp after being convicted of conspiracy to obstruct, obstruction of justice, two counts of false statements to a grand jury and one count of perjury?

The trade paper describes Mr. Mitchell as "dean of bond counsel," which should thrill those still-practicing lawyers who pride themselves in this line of work. And there's nothing like an exceptionally crude racial slur to get an opinion across in a hurry. Still, there are a few pertinent things that happened at the District Building while Prisoner No. 24171-157 was doing time on the banks of the Alabama River. Most notable, perhaps, was the transition of the D.C. government to a nationally recognized sound financial-management footing -- greatly better than that of the federal government during Mr. Mitchell's time in the Cabinet.

At last report, in fact, the D.C. government completed the fiscal year, on Sept. 30, with a balanced operating budget with money left over to help reduce its accumulated deficit. The latest statistics, incidentally, come from a prospectus prepared by Salomon Bros. Inc. of New York City and five other companies that served as the underwriters of $150 million of short-term notes recently marketed by the District. The District also received the highest rating on its note from Standard & Poor's Corp. and Moody's Investors Service -- no pikers when it comes to municipal bond-rating services.

Speaking of ratings and qualifications, John Mitchell's fitness to comment on any of this is about Triple Z.