PARIS — French Muslims have been officially invisible, expected to blend in with the rest of the citizenry in secular France. But now they are speaking out — and being called on to take a larger role in combatting the threat from Islamist extremists.

The killing of a priest last week at the altar of his Normandy church by two 19-year-old extremists has become a lightning rod for change.

In an unusual joint statement published Sunday, a group of more than 40 Muslim lawyers, doctors and other professionals said that French Muslims must move from the shadows to front and center, and take action because those representing Islam have lost touch with the young.

“We were silent because we learned that in France religion is a private affair,” the signers wrote, referring to the secular values France prizes and the French model of integration by which citizens forego their cultures of origin for Frenchness. “Now we must speak because Islam has become a public affair and the current situation is intolerable.”

The signers said Muslim leaders are unable to reach out, let alone represent, a younger generation of Muslims — some of them “the prey of jihadi Islam ideologues.”

France’s strict brand of secularism was behind two laws to ban Muslim apparel — headscarves in classrooms in 2004 and face-covering veils in streets, in 2010. It has also meant French authorities normally communicate only with Muslim leaders through the French Council for the Muslim Faith, or CFCM — an umbrella group the government helped set up in 2003 as conduit for dialogue with a religion that, unlike Catholicism, has no hierarchy.

But now, even the government is reaching beyond Muslim officialdom to implore citizens of the Islamic faith to join in the battle for hearts and minds against extremists.