Nicolas Sarkozy pushed through France’s pension reforms in 2010, but it was a hard-fought battle.

Plans to increase the retirement age from 60 to 62 were bitterly opposed by the labor unions through a series of well-attended strikes, but the French president knew there was too much at stake for him to give in. France has not enjoyed a budget surplus since 1974 because of high public spending, and unusually high expenditure on pensions has contributed greatly to this persistent structural deficit. This made the increase in the retirement age an important triumph in France’s search for fiscal soundness — which has become even more urgent since 2010.

But now this achievement is at risk of unraveling — raising questions about France’s ability to control its high government debt. François Hollande, the Socialist candidate and clear frontrunner in the race to become French president, has said he will restore the retirement age to 60. In the first round of the election, held Sunday, he polled 28.5 — compared with 27.1 percent for Sarkozy, who belongs to the center-right Union for a Popular Movement Party. But in the second and final round — on May 6 — Hollande is expected to win by a wide margin.