PARIS — The debate is now so heated in France that one could be forgiven for assuming that the burkini — the full-body bathing suit worn by some Muslim women — had invaded French beaches. Five towns have banned them. Three more are in the process of doing so. Prime Minister Manuel Valls supported the prohibitions on Wednesday, calling the garment part of “the enslavement of women.”

In fact it would be challenging to spot a burkini on most French beaches, and even some of the mayors considering the bans admit to never having seen one.

But with a presidential election approaching next year, and the nation palpably on edge after a series of terrorist attacks — including 85 people killed this summer along the French Riviera — the burkini has become a new dividing line in France’s increasingly fraught relationship with its Muslim population, Europe’s largest.

That there is no clear definition of what qualifies as a burkini, and that Muslim women have complained of being singled out on beaches even when covered by other kinds of garments, has raised the question of whether the increasing number of bans are meant to signal France’s demand for conformity with its non-Muslim majority or are genuinely part of France’s culture of laïcité, or secularism in public life.

That debate is a continuation of deep-seated discomfort in France with Muslim women’s dress that has long defied simple categories of left and right, leaving Mr. Valls, a Socialist, sounding a lot like the presidential hopeful for the center-right, Nicolas Sarkozy, or for that matter, Marine Le Pen, the leader of the extreme-right National Front.

“This is the soul of France that is in question,” Ms. Le Pen wrote in a blog post that strongly supported the burkini ban. “France does not lock away a woman’s body, France does not hide half of its population under the fallacious and hateful pretext that the other half fears it will be tempted.”

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In Cannes, where a ban on the burkini was enacted last week, at least six of 10 women who complained to a local Muslim association were simply going into the sea with their bodies covered. Violators of the ban are asked to leave the beach and can be fined 38 euros, or about $42.

On Saturday, brawls broke out at a beach in Corsica after some beachgoers began taking photographs of Muslim women wearing burkinis, prompting the mayor of the town of Sisco to ban the full-body bathing suits.