Mayor Marion Barry sidestepped an appointment to carry a copy of the District of Columbia citizenry's nuclear freeze initiative to Capitol Hill yesterday so he could damp down a potentially explosive problem down the hall from his own office.

As you can read elsewhere in today's paper, Barry was appearing before the City Council to explain--or, as some council members perceived, to explain away--some of the findings of the latest audit of the city books.

At 12:52, Council Chairman David A. Clarke observed that the mayor had to break off at 1 o'clock to drive to the Capitol to join representatives of four states presenting nuclear freeze initiatives that were adopted last November to House Speaker Tip O'Neill. Washingtonians, shunning opposition to such measures by the Reagan administration, adopted the nonbinding freeze measure by a vote of about 80,000 to 35,000.

Hearing of the mayor's appointment, council member Polly Shackleton (D-Ward 3) said she'd forgo her questions so Barry could make the important trip.

But Barry said it already was too late. "I sent my staff to take it," he said.

So Barry continued to face the council members. Judging from some of the barbed rhetoric, he might've done better with the Speaker.

Incidentally, if you see hizzoner on the TV tube and view a round button on his right lapel, it's the emblem of the University of the District of Columbia.