PARIS — Shocked by the carnage of the Paris attacks, France and Belgium moved aggressively on Thursday to strengthen the hand of their security forces, pushing Europe more deeply into a debate that has raged in the United States since Sept. 11, 2001: how to balance counterterrorism efforts and civil liberties.

With their populations stunned and nervous and political pressure growing on the right, the French and Belgian governments made it clear that, for now, they would put protecting their citizens ahead of other considerations.

With time, the United States has moved to ease some elements of the U.S.A. Patriot Act, passed in the aftermath of the Sept. 11 attacks. It has also strengthened oversight of intelligence agencies and of mass domestic surveillance in the wake of the revelations by Edward J. Snowden, the former contractor for the National Security Agency who leaked documents about surveillance.

But European nations battered by terrorism are moving in the other direction. Those nations include France, which has suffered multiple attacks this year; Belgium, where many of the Paris attackers lived or grew up; and Britain, which has thwarted a number of plots in recent years. Each is updating and strengthening government power while debating further controls over passport-free travel within continental Europe.