Three sourpuss Parks Department agents put the squeeze on a 10-year-old girl in Riverside Park yesterday, slapping the tyke with a $50 ticket for hawking lemonade without a permit.

Clementine Lee, who lives just blocks from the Upper West Side park, had dreamed of opening a lemonade stand since last year and took advantage of yesterday’s beautiful weather to set up shop.

“It was such a hot day I figured people would want a cold drink,” the aspiring juvenile juice mogul told The Post.

Business was booming for Clementine and her photographer dad, Richard, 49, for the first 20 minutes at the stand on West 73rd Street and Riverside Drive.

The father-daughter team was able to sell 10 glasses of the ice-cold drink for 50 cents each and the dozen chocolate chip cookies they baked.

But their day turned into the pits at 3 p.m. when the heartless pack of city sticklers iced their operation.

“They approached us nonchalantly but then surrounded us,” the peeved papa recalled. “They were very hostile as soon as they approached, saying ‘Where’s your permit? Where’s your permit?’ ”

When Richard admitted he didn’t have the right to sell on Parks property, the agents immediately slapped the dad and daughter with a summons for selling food without a license, which carries a maximum fine of $200.

“You’ve got to be kidding me, this is outrageous!” he told the agents.

Dozens of onlookers rallied to the pair’s defense, shouting that the Parks officers were violating the Lees’ civil rights, but the brokenhearted pair packed up and went home.

“Don’t these agents have anything better to do?” Richard fumed to The Post. “They could have at least told us to move but they didn’t give us a chance.

“There are better ways to raise money for the Parks Department then busting 10 year-olds.”

His soccer-enthusiast daughter said the ordeal left a bitter taste in her mouth.

“I was really nervous when these three agents cornered me and my dad,” said Clementine, who loves classical music and has been playing violin since she was 4.

“I think they should let people sell lemonade out here. We weren’t hurting anyone.”

But yesterday, after The Post contacted the department, Parks Commissioner Adrian Benepe announced that the ticket would be nixed.

“The agent used extremely poor judgment” and didn’t properly enforce the rule, Benepe said.

The bumbling Parks enforcement patrol officer will be re-trained on rules and regulations and will be reassigned, he added.

“We’re going to make lemonade out of lemons . . . I look forward to buying lemonade from her if I pass by,” said the commissioner.

Clementine said she might take him up on the offer.

“I’m going to wait a little while, but I’d love to [sell lemonade] again,” she said.

As for her dad, he was relieved that “justice was served.”

tim.perone@nypost.com