MADRID, Spain — Spaniards yesterday re-elected Prime Minister Jose Luis Rodriguez Zapatero and the ruling Socialist Party, turning out in large numbers following an acrimonious campaign that accented deep divisions in Spanish society.

But the Socialists defeated the right-wing Popular Party by a narrow margin and fell short of gaining an absolute majority in the lower house of parliament. That could hamper their ability to govern and foreshadow another four-year term possibly as contentious as the one coming to an end.

Waving red-and-white party flags and chanting the name of their leader, jubilant Socialists celebrated outside their party headquarters in Madrid and across the country. Spain’s last national elections, in 2004, came three days after the country suffered continental Europe’s deadliest terror attack.

“The Spanish people have spoken clearly,” Mr. Zapatero said in a victory speech to the crowd. “They have agreed that it is time to open a new era, a new era without the hostilities, an era that excludes confrontation and seeks agreement.” A politician not known for his charisma, Mr. Zapatero, 47, beamed as he pledged to pursue the liberal social reforms that he launched in his first term but also to “correct mistakes,” offering “a firm hand, but an outstretched hand.”

At the Popular Party headquarters, supporters were as noisy as if they had won. The party’s prime ministerial candidate, Mariano Rajoy, and other party leaders conceded defeat but pledged to continue waging a sharp opposition.