Ms. Le Pen depicted a France with a “total collapse of our industries,” preyed upon by Islamist extremists, demanding ever more government protection from economic vicissitudes and urgently needing to close its borders. “I’m the candidate of that France that we love, who will protect our frontiers, who will protect us from savage globalization,” she said at the outset.

Mr. Macron was a ruthless capitalist in Ms. Le Pen’s familiar neo-populist depiction, ready to sell French industry down the river to hurt workers and help employers. She repeatedly tied Mr. Macron to the failed government of the incumbent Socialist president, François Hollande, in which Mr. Macron served for two years before quitting to start his own political movement.

“You defend private interests,” Ms. Le Pen sneered. “And behind that there is social ruin.”

Mr. Macron replied evenly, “What’s extraordinary is that your strategy is simply to say a lot of lies and propose nothing to help the country.” He pointed out the weaknesses in her generous spending plans, noting the lack of revenue-raising measures to back them. “France and the French deserve better,” he said. “Don’t say stupid things. You are saying a lot of them.”

Some of the sharpest exchanges came over terrorism, which polls show is a major preoccupation for the French. Ms. Le Pen cast herself as tougher on the issue, reeling off a series of antiterrorism measures — experts have suggested that they are either impractical or ineffective — and saying Mr. Macron was a weakling on security. Nonetheless, it is one of her signature issues, always drawing a thunderous response when she invokes it at rallies. “You are for laxism,” Ms. Le Pen said.