Vladimir Putin’s return to the Russian presidency comes at a delicate time when North Korea’s move toward a third nuclear test is alerting neighboring powers, with the U.S. and China engaged in an increasing military rivalry in the Pacific region.

Putin, who began his third presidential term Monday, may well expect this situation to give him more leeway in expanding Russia’s strategic presence in Northeast Asia.

He had kept his grip on power while serving as prime minister during the past four years. But in his capacity as head of state again, Putin is expected to become more aggressive to reestablish Russia’s status as a key regional player.

In the face of growing domestic discontent with his heavy-handed rule, a successful push to enhance Russia’s international prestige would help shore up Putin’s declining popularity at home.

Though arguably in a weaker position than he first came to power more than 12 years ago, a mandate to govern for another six years gives him a stronger diplomatic hand than other regional leaders, who will step down or bid for reelection in the coming months.

Chinese President Hu Jintao is set to hand over the top leadership post to Vice President Xi Jinping during a party congress this fall and South Korean President Lee Myung-bak leaves office in early 2013, ending his single five-year term.

U.S. President Barack Obama is bidding to win reelection in November on records that are less than convincing to voters, while Japanese Prime Minister Yoshihiko Noda may also put his job at stake by calling snap elections, probably in August if parliament blocks the bill to hike the consumption tax.

Putin’s relatively stable position will be conspicuous when he hosts other regional leaders at the Asia-Pacific Economic Cooperation summit in Vladivostok, a port city in the Russian Far East, in September. He will naturally make the best use of it as a valuable occasion to heighten Russia’s stature as an Asian power.

When he first took the helm of Russia at the turn of the millennium, Putin sought a mediating role in settling tensions on the Korean Peninsula. He visited Pyongyang in July 2000 and traveled to Seoul in February 2001. He received then North Korean leader Kim Jong-il in Moscow in August 2001 before they met again in Vladivostok a year later.

Although the exchanges bore little fruit because of Pyongyang’s provocative stance, Putin’s attempt to mediate in the standoff with the isolated regime reflected his activeness in promoting Moscow’s influence in areas of strategic importance during his first two presidential terms in 2000-08.

Now he is back at the Kremlin, he will likely seek to reactivate Moscow’s role in helping ease tensions on the peninsula and thus forge favorable conditions for projects involving Russia and the two Koreas.

Putin is thought to consider focusing on trilateral schemes such as a natural gas pipeline passing through the three nations as a most effective way to strengthen Russia’s strategic presence in Northeast Asia beyond the Korean Peninsula.

Under his rule, Russia is also expected to further enhance bilateral cooperation with South Korea, whose investment and technology are needed to carry out his plans to develop resources, build infrastructure and modernize industrial structure.

Putin’s aggressive approach would certainly be something both policymakers and business leaders here should consider embracing in a corresponding manner.

Considering Russia’s pragmatic intent in handling peninsular issues, South Korea might be placed to benefit from leaving the mediating role to Putin. In close step with Seoul, Moscow could be conducive to resolving the dispute with Pyongyang and encouraging the isolated regime toward reform and openness.

Broader ties with Russia might also help South Korea increase its leverage with China and supplement its reliance on the U.S.

South Korean businesses are advised to take a long-term approach to form a comprehensive partnership with Russia, instead of being preoccupied with energy and resources projects.

Under Putin’s reign, Russia is expected to close ranks with China in confronting the U.S. in the Pacific region, as signaled by the first-ever joint drill by the navies of the two countries in the Yellow Sea last month.

Putin has made no secret of his view that China is less aggressive globally than the U.S.

Seoul officials, especially in the next administration, might find it more necessary ― and more difficult ― to walk a fine line between the U.S. and a China supported by Russia amid their escalating military rivalry.