Japanese Prime Minister and President of the Liberal Democratic Party (LDP), Shinzo Abe celebrates his party's win after he placed a red paper rose on a LDP candidate's name to indicate an election victory at the party's headquarters in Tokyo on July 21, 2013. Voters gave Prime Minister Shinzo Abe a resounding victory in upper house elections exit polls showed. (Kazuhiro Nogi/AFP/Getty Images)

Japanese voters dealt a runaway election victory Sunday to the ruling Liberal Democratic Party, in a strong sign of approval for Prime Minister Shinzo Abe’s ambitious plan to revive the world’s third-largest economy.

Sunday’s vote, for seats in the upper house of parliament, gives Abe’s ruling bloc control of both chambers — and it provides Abe with a mandate unmatched by any Japanese leader in nearly a decade.

How Abe uses that political power will help determine the long-term health of Japan’s economy and its relations with Asian neighbors. Analysts say Abe could pursue a largely economic agenda, one that includes difficult but needed reforms and austerity measures. But Abe, known as a strong nationalist, also could feel emboldened to speak more openly about his revisionist view of Asian history, one that rejects the idea of Japanese imperial invasion and infuriates China and South ­Korea.

In this election, only half of the 242 seats in the upper house were up for grabs. According to final results announced early Monday, the LDP and coalition partner New Komeito together claimed 76 seats — giving them total of 135 in the chamber, a comfortable majority. The LDP won 65 of those seats, just shy of the 72 it would have needed to form a majority on its own.

“We received so much support from the people of Japan,” Abe said in a victory speech at his party’s headquarters. “We now have to move politics forward.”

Japan isn’t required by law to hold another parliamentary election for three years, and pundits say Abe could go as long as that without a challenge to his power, provided he maintains support from his own party. Such stability would mark a fundamental shift for a nation that has cycled through seven leaders since 2006, none lasting longer than 481 days in office. Abe was one of those short-term leaders, holding power for a scandal-filled year before resigning in September 2007 because of an intestinal ailment, his approval rating below 30 percent.

Abe says he has learned from that stint, and in his second chance at the job — beginning seven months ago — he has spent less time on nationalist pet projects, devoting himself instead to the issue that Japanese voters care most about: the economy.

With full-throttle monetary easing and fiscal stimulus, Abe has lowered the value of the yen and driven up the stock market, all as companies rake in profits and business confidence soars. Average consumers haven’t seen the benefits — they will, Abe promises — but they say they like the ambition of Abe’s policy­making.

As part of his economic revival plan, Abe has pledged a set of reforms. One batch, unveiled before the election, left investors unimpressed. But economists hope that Abe can use his political capital to overhaul the pension system, free companies to more easily hire and fire workers, and clear away some of Japan’s burdensome government debt. Japan has a “three-year window to start fiscal consolidation and structural reform,” Barclays Bank researchers wrote in a note to investors.

Abe on Sunday night said his party’s real test is set to begin. “I believe people want the economic policies to [give them] something tangible,” he said.

But some opposition policymakers in Japan warn that Abe could focus on right-wing goals, a more controversial agenda that includes patriotic education for youngsters and looser restrictions on Japan’s Self-Defense Forces. Abe also could take a harder approach with China amid a fierce dispute over a small island chain. During a rare trip last week to Japan’s front-line islands, Abe said the “security environment facing Japan is becoming ever more severe.”

Whatever his next steps, Abe will have an easier time taking them than previous leaders, who contended with a “twisted Diet” where different parties ruled the two chambers. Now, Japan again looks much like a one-party state — a throwback to the ­half-century following World War II, when the LDP ruled almost without interruption.

The LDP that guided Japan’s postwar rise was a monolith. It straddled the left and right. It spent on massive public works projects and engineered a manufacturing-driven economic miracle. It held support from farmers and housewives, executives and bureaucrats.

Between 2009 and December 2012, the LDP was on the sidelines, booted from power by voters frustrated with its inability to fix a stagnant economy. Analysts say that this time around, the LDP isn’t nearly as entrenched as it used to be.

But it has managed to rebuild support among Japan’s major bloc of unaffiliated voters. According to opinion polling from national public broadcaster NHK, the LDP’s approval rating a year ago was 20 percent; more than 50 percent supported no party at all. Now, 43 percent support the LDP — and no other party has an approval rating higher than 8 percent.

Those minority parties have self-inflicted wounds. The Democratic Party of Japan, which ruled during the LDP’s retreat, was undone by three prime ministers who pursued opposite policies. The recently formed Japan Restoration Party lost its support in short order, undone by remarks from one of its leaders, an iconoclastic right-winger who said that sex slaves were “necessary” for Japanese soldiers during war. The DPJ — which held 44 of the 121 seats up for grabs — managed to win back 17. The Japan Restoration Party won eight.

Yuki Oda contributed to this report.