Mr. Abe has vowed to encourage growth quickly by offering 10 trillion yen, or about $120 billion, in public works and other emergency stimulus spending. He has also promised to force the central bank to move more aggressively to combat deflation and to weaken the value of the yen, actions that would offer relief to beleaguered export industries by making Japanese products cheaper abroad.

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The measures are intended to revive the economy ahead of the elections in June, to give Mr. Abe’s party a better chance of winning the upper house and, with it, control of Parliament. Mr. Abe will have to hurry to retain the support of Japan’s weary voters, who have shown themselves quick to turn against leaders who fail to deliver on promises of change.

Immediately after the vote on Wednesday, Mr. Abe began appointing a cabinet filled with relatively young and unknown faces. While many of these appointees are Mr. Abe’s friends, the fresh lineup is also apparently intended to emphasize that the party has changed since it was driven from power three years ago.

Among the few veterans in the cabinet is Taro Aso, 72, a former prime minister, who was appointed finance minister. The post of foreign minister went to Fumio Kishida, 55, a former minister in charge of Okinawan affairs. He is expected to try to smooth ties with the United States, which have been frayed by a dispute over an American air base on Okinawa.

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Mr. Abe will face other early challenges, like bridging a rift within his party over whether Japan should join a new regional free-trade agreement led by the United States. The pact, called the Trans-Pacific Partnership, is supported by business leaders but opposed by farmers, two groups that are among the staunchest supporters of the Liberal Democrats.

Another challenge will be responding to China’s stepped-up efforts to assert its claims to the disputed islands, which Japan calls the Senkaku and China calls the Diaoyu. Chinese ships and, more recently, aircraft now make almost daily incursions into Japanese-controlled waters and airspace near the islands, with no signs of letting up.

Mr. Abe has been vague about whether he will shift his energies to his long-held desire to rewrite Japan’s antiwar Constitution to allow for a full-fledged military.

Mr. Abe and other conservatives say such a step is needed for Japan to stand up for itself in light of China’s growing strength, and to share more of the regional security burden with the United States. However, the move could also be seen as provocative by China and South Korea, two victims of Japan’s World War II-era militaristic policies.