Vice President Mondale spent yesterday making a kind of ethnic tour of New York City -- which the Carter camp considers vital to its hopes of defeating Republican nominee Ronald Reagan in November.

Accompanied by New York Gov. Hugh Carey and New York City Mayor Edward Koch, both of whom are now firmly back in the Carter fold, Mondale attended a U.N. ceremony dedicating a sculpture and and park to black American diplomat Ralph Bunch, a gathering of Hispanic women who support Carter's reelection and the Feast of San Gennaro, a festive Italian street fair on Manhattan's Lower East Side.

"This fight in this country [in November] will be all over the nation, but nowhere will it be more strongly contested than here in "New York," Mondale told the Hispanic women. "What you decide will decide who is sworn in next January."

The Carter-Mondale campaign has been concerned about a possible slippage of votes in New York in November, with some ethnic and blue collar support threatening to defeat from the Democratic Party, and many Jewish voters -- who make up almost a third of New York's electorate -- preferring independent candidate John B. Anderson. New York's electoral votes are considered crucial for a Carter victory.