A gunman was shot dead in Paris on Thursday after killing a policeman.
Ms Le Pen has pledged to expel radical Islamists and restore border checks.
Another frontrunner, Emmanuel Macron, stressed that France must not panic, because that would play into the terrorists' hands.
The late-night attack on the capital's famous Champs Elysees Avenue, which also left two officers wounded, made security a pressing issue ahead of Sunday's first round of voting in the presidential election.
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The main candidates called off rallies on what would have been the final day of campaigning.
Former conservative Prime Minister FranÃ§ois Fillon said the next president's priority should be fighting "Islamist totalitarianism".
Ms Le Pen, leader of the National Front (FN), called for France's border controls to be reinstated immediately, and for foreigners on security watch lists to be expelled.
Security officials say the gunman was known to them and his home in Chelles, in the eastern suburbs of Paris, has been searched. He had been identified as a potential radical Islamist.
The so-called Islamic State group has said it was behind the attack in Paris - a city still scarred by bloody IS attacks in 2015.
"We must fight barbarism - none of the French governments for the past 10 years has done enough," Ms Le Pen said.
She spoke of "incredible lapses in the justice system".
Speaking on RTL radio, the liberal centrist Mr Macron told French voters they should "not allow fear to be exploited" by terrorists.
"The assailants want death, symbolism, to sow panic, to disrupt the democratic process - the presidential election," he said.
An Elabe opinion poll, carried out before the shooting on the Champs Elysees, showed Mr Macron with 24% in the first round, and Ms Le Pen falling back slightly to 21.5%.
Mr Fillon was close behind on 20% and the far left's Jean-Luc MÃ©lenchon on 19.5%.
The far-right presidential candidate in France, Marine Le Pen, has condemned what she calls security lapses, as the nation prepares to vote in the shadow of a terror attack.