The discussion was at times chaotic and dominated by the anti-capitalist and virulently anti-EU smaller candidates who made their first major appearance ahead of the first round of the two-stage vote on April 23.
The most telling clash between the frontrunners came at the end of the first section when 39-year-old Macron took on what is considered one of Le Pen's vulnerabilities -- her plans to scrap the euro and revert to the franc.
Polls show only a third of French voters support scrapping the euro, many of them anxious about the impact of a devaluation which would hit their savings and spur inflation.
The clash and Macron's more combative performance could point to the tone and shape of the campaign ahead, with Macron and Le Pen having emerged as the clear frontrunners.
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Macron accused her of wanting to start an "economic war" with France's neighbours and denounced her nationalist stance, which he said had torn the continent apart in the past and filled graveyards near his hometown Amiens in northeast France.
Polls show far-right candidate Le Pen and centrist independent Macron in a dead heat at around 25 percent heading into the first round on April 23. Macron is seen easily winning the second round on May 7.
Le Pen put in a steady performance under fire, warning about the closure of factories, and the danger of Islamists and immigrants eroding France's national identity.
"I consider that in this election our civilisation is at stake," she said at the start of the debate, promising to restore order and combat "unfettered globalisation".
Socialist candidate Benoit Hamon scoffed at her defence, saying it was "amusing to see you playing the victim while spending your time attacking immigrants".
For the second time, Hamon found himself eclipsed by his rising far-left rival Jean-Luc Melenchon, who put in another assured performance, according to a poll published by BFM television after the debate.
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