French President Nicolas Sarkozy has promised to ban militant Muslim preachers from entering the country.
The measure is part of a crackdown following recent attacks by a gunman who claimed to be a member of al-Qaeda.
Mr Sarkozy said he would not allow militant preachers to attend an Islamic conference due to take place in April.
The first round of the presidential election takes place next month, and Mr Sarkozy is neck and neck in the polls with Socialist rival Francois Hollande.
As part of a round of media interviews in the run up to the polls, he highlighted a forthcoming conference to be held by the Union of Islamic Organisations in France.
"There are certain people who have been invited to this congress who are not welcome on French soil," he said.
He singled out Youssef al-Qaradawi, an Egyptian Sunni Muslim cleric who is based in Qatar.
He holds a diplomatic passport, and requires no visa to enter France. But Mr Sarkozy says he has spoken to the Emir of Qatar, and the cleric will not be allowed to leave for France.
In the past Mr Qaradawi has defended Palestinian suicide bombers in Israel, and attacks on US forces in Iraq. He was denied entry to the UK in 2008.
Mr Sarkozy had been trailing in the opinion polls behind Mr Hollande.
But he has gained ground following the killing last week of Mohammed Merah, a self-proclaimed al-Qaeda supporter who murdered three paratroopers and four Jewish civilians in a series of shootings that shocked France.
In the immediate aftermath of Merah's death Mr Sarkozy announced plans to make it a crime to repeatedly consult internet sites advocating Islamic extremism, and to punish those who travel overseas for indoctrination or terrorist training.
He also attacked the far-right National Front candidate, Marine Le Pen.
She has attempted to link Merah's actions to immigration, but Mr Sarkozy said it made "no sense" to connect the crimes with either immigration or Islam, because Merah was born and brought up in France.