"It's no longer a nation but a splintered multicultural society... where the only law is the survival of the fittest," said Le Pen, who got fresh bad news Thursday in the "fake jobs" scandal afflicting her National Front (FN) party.
"This election is a referendum for or against France... I'm asking you to choose France," she said.
But Le Pen, who the latest polls suggest is some 20 points behind her rival, also sought to cast a reassuring image aimed at broadening voter support for her anti-immigrant, anti-EU camp.
"I pay no attention to your origins, your religion, your sexual orientation, the colour of your skin," she told the flag-waving crowd. "That doesn't interest me, what interests me is you."
She has campaigned fiercely since she and Macron qualified Sunday for the runoff, while Macron was accused of a laggardly start to his second-round efforts but has stepped up the pace over the past 24 hours.
'Neither banker, nor racist'
The former economy minister, speaking at nearly the same time as Le Pen on French television, said he aimed to heal the divide in France over its relationship with the EU.
"I will defend (the EU) by reforming it," he said. "Our challenge is to reconcile our citizens with the EU... which we need to provide more protection to our citizens amid globalisation."
Macron was booed and heckled on Wednesday when he visited a Whirlpool factory in the northern city of Amiens, his hometown, where the US appliances giant is threatening to partially outsource production to Poland.
The besuited candidate had been meeting with union representatives kilometres away from the plant, but he was upstaged when Le Pen showed up at the factory unannounced.
Her appearance forced a hasty change in plans and Macron ended up spending more than an hour debating with workers amid chaotic scenes as dozens of TV camera teams crowded around him.
He left the incident relatively unscathed, and even shook hands with some workers before leaving.
Macron and Le Pen topped the first round of the election on Sunday to advance to the runoff, but not everyone is happy with the line-up.
On Thursday, students demonstrating against both candidates clashed with police in Paris, hurled bottles at the officers who responded with tear gas.
Black-clad demonstrators broke off from a 1,000-strong crowd of mostly teens waving signs that said "Neither the banker, nor the racist".
The latest poll suggests Macron will defeat Le Pen by a margin of 21 points in the runoff on May 7, and figures from France's traditional left and right -- both absent from the second round -- have backed him too.
Le Pen journeyed to the Mediterranean coast Thursday to spend the morning aboard a fishing trawler, seeking to portray herself as the protector of small-time producers.
- Five million euros -
The "Battle of Amiens" at the Whirlpool factory -- as leftwing daily Liberation called it -- was the standout moment of the election so far, even though the candidates were not at the site at the same time.
Much of campaign was dominated by the legal woes engulfing conservative Francois Fillon, whose campaign was dogged by allegations he paid his wife millions in public money for little work. He lost in Sunday's first round.
But on Thursday there was a reminder of the allegations of wrongdoing also hanging over Le Pen.
Investigators probing alleged FN expenses fraud at the European Parliament said the sum involved was now believed to be nearly five million euros ($5.5 million), more than twice an initial estimate.
The parliament accuses the FN of using funds meant for parliamentary assistants to pay staff including a bodyguard to work in France between 2012 and 2017, which contravenes the assembly's rules.
In March, Le Pen invoked her immunity as an MEP in refusing to submit to questioning by French prosecutors until after the election.
"Five million euros, that's nonsense," said Wallerand de Saint Just, National Front party treasurer.