At mid-morning today, Baltimore City Councilman Dominic M. DiPietro stood in a vacant lot that is soon to be transformed into a park honoring Christopher Columbus and assured a visitor that President Reagan's visit to dedicate a statue to the discoverer of America would be a non-partisan event.

"Do you see anything political around here?" asked DiPietro, his arm sweeping in an arc towards Little Italy to the east.

Any hopes this city's Italian American community had for keeping its ceremony from turning into a political event were dashed when the first busloads of Reagan supporters began to unload in the cramped streets of Little Italy. About a quarter of the 4,000 people who wedged themselves into the Columbus Piazza were brought in by the state Republican Party.

And, although Baltimore Mayor William Donald Schaefer introduced the president, many of the state's top Democratic officeholders stayed away. Among those absent was Gov. Harry Hughes, who was said to be preparing for an economic development trip to Western Maryland.

When Reagan tugged on a felt rope and unveiled the 14-foot, 17-ton statue of white Carrara marble, the Columbus Piazza was a sea of Republican partisanship, with signs reading "Moscow loves Mondale" and "Unborn Babies Love Reagan" bobbing in the currents.

"I'm here to enjoy this non-partisan event," said a grinning State Sen. Howard A. Denis, a Republican legislator from Montgomery County who carried in one hand an Italian flag and in the other a blue and white sign that said Reagan in English and Hebrew.

DiPietro, who is a Democrat, and other members of the committee that raised funds for the Columbus statue and invited the president to participate last June said they worked overtime to keep today's festivities presidential rather than electoral.

When it was learned that Helen Bentley, the Republican candidate for Congress in Maryland's second district was to share the podium with Reagan and other dignitaries, DiPietro asked the White House to keep her away. "I'm going to run her off if she comes," growled DiPietro.

But DiPietro and the other sons of this city's Little Italy community were unable to muzzle the Republican candidate for president just 29 days before the November election and one day after a debate with Democratic nominee Walter F. Mondale.

"Those who have never broken free from the mentality of tax, tax, spend, spend, still think increasing taxes is the best way to solve America's problems," said Reagan in a 15-minute address that used Columbus' daring voyage as a parable for extolling Republican virtues.

"The old welfare state did not work," he proclaimed. "We don't need the failed federal programs that create dependency and leave people in despair."

How Reagan will fare among this city's Italian American community was a subject of considerable debate today.

Little Italy, which went 2 to 1 for Jimmy Carter in 1980, has now had visits from both Reagan and Democratic vice presidential nominee Geraldine A. Ferraro, who passed through two weeks ago. (She drew a slightly larger crowd at a downtown location where she made her main appearance.)

And if the event's organizers got a little less Columbus and a little more rhetoric than they had bargained for, many others got what they wanted.

As one out-of-town visitor, a civilian employe for the Navy who asked not to be named, observed: "I wanted to see the phenomenon in action."