Mitt Romney declared he was proud to have “a Koch problem,” as he attended a $50,000-a-head fund-raiser hosted by conservative billionaire David Koch.

A plane flew over the Hamptons with a banner from protestors reading, “Mitt Romney has a Koch problem,” as he stopped for three major fund-raisers Sunday — first at the East Hampton home of billionaire Ronald Perelman, followed by events at the home of Clifford Sobel, the former US ambassador to Brazil, then for dinner at David and Julia Koch’s home on Meadow Lane in Southampton.

Romney quipped to the crowd at Koch’s event, “I understand there is a plane out there saying Mitt Romney has ‘a Koch problem.’ I don’t look at it as a problem; I look at it as an asset.”

Koch was given a private audience with Romney before the event started, heading upstairs with their wives for a personal meeting for 30 minutes before “descending back down like two world leaders with their first ladies,” quipped one attendee.

Introducing Romney to the guests — who included Miami Marlin owner Jeffrey Loria, former Ambassador to Jamaica Brenda LaGrange Johnson and Randy Altschuler — David Koch said, “We can’t afford these levels of debt . . . We don’t want to end up bankrupt like Greece.”

Romney stayed for dinner — tomato and mozzarella corn fritters, chicken and arugula salad and cupcakes and ice cream for dessert — served on the Koch couple’s wedding tablecloths, “a simple meal to make sure the most money raised goes to the campaign,” said a source.

New York Jet owner Woody Johnson, one of Romney’s major bundlers, was present at all three events, which were estimated to have raised more than $3 million, witnesses said.

Earlier — at the Sobels’ $25,000-a-ticket bash attended by John

Catsimatidis, Dr. Nicholas Perricone and David Schwartz — Romney said, “If you are here, by and large, you are doing just fine . . . I spend a lot of time worrying about those that are poor and those in the middle class.”