TOKYO, Japan — If the enemy of one's enemy is a friend, then Japan and South Korea are growing ever closer. It is a drama in which U.S. Defense Secretary Robert Gates plays a starring role this week.

Gates is the latest and possibly the most influential U.S. official to make the rounds in northeast Asia. Though he has not mentioned a trilateral alliance outright among Tokyo, Seoul and Washington, he has made efforts to buttress separate U.S. alliances with each. And Gates has taken care to highlight the common enemy, North Korea.

On his three-day trip to Beijing, during which Gates was greeted to an unexpected show of force when China debuted its stealth fighter, Gates stressed that North Korea now poses an imminent threat to the United States. North Korea, he said, will soon have a missile capable of reaching Hawaii or Alaska.

Gates in Japan Thursday further emphasized North Korea's status as a threat by poking and prodding Tokyo to take on more of a leadership role in reining in the rogue nation. He even went so far as to suggest that Japan purchase Lockheed Martin fighter jets, the first such public suggestion by a U.S. military official.

It was the theme of "common interest" as emphasized by Gates that came closest to hinting at triltateralism — and even the mystical U.S.-Japan-Korea trilateral alliance.

Gates, harping on that theme Thurday with Japan's defense minister, Toshimi Kitazawa, clearly assumed the Japanese should fully agree on the need for unity against North Korea. He also saw China as sharing a similar interest but from a very different perspective — as North Korea's only ally, the source of all the North's fuel and much of its food and the only power with direct influence inside Pyongyang.

Gates' odyssey will culminate Friday in Seoul with the usual affirmations of U.S. support against attack, all calculated to show the strength of Washington’s commitment without ruling out reconciliation.

Stakes are high, since the missile North Korea is supposedly developing may ultimately be capable of delivering a weapon of mass destruction, though the North is believed to be a ways from reaching that goal. The last time it tested a long-range missile, it flew more than 2,000 miles carrying what was said to be a satellite, though whatever it was plunged into the Pacific without going into orbit.

Gates and Kitazawa talked about “strategic goals” amid rising concerns about the North, just a few days after Kitazawa was in Seoul discussing two historic agreements that could lead to closer military ties between Japan and South Korea.

The first would be an agreement by which Japan and South Korea share supplies and servicing of equipment during joint military exercises. The second, perhaps more ominous, agreement would be a military information deal under which they would share intelligence — that is, military secrets.

In Japan, Gates had to navigate popular sentiment against a U.S. base in Okinawa, which has focused on deadlock over relocating the base to a remote corner of the island. According to a 2006 agreement, the United States is entitled to build another base on Okinawa, though voters oppose the plan.

North Korea's recent aggressions in the Yellow Sea, however, have almost certainly ensured that Japan's Prime Minister Naoto Kan will allow the U.S. to go ahead and build the new base. The Japanese remember when North Korea kidnapped dozens of their citizens not 30 years ago. They must wonder what the North is capable of now after sinking a South Korean ship in March and shelling Yeonpyeong in November.

Even if Gates is not thwarted overtly by controversy in Okinawa, which he has downplayed, there is the risk he will be upstaged by North Korea directly. The counterpoint to his talks this week has been the North's call for negotiations, ranging from six-party talks in Beijing to bilateral meetings with South Korea and Japan.

North Korea’s proposal is part of a bargaining game over talks it has said should be held “without conditions.” Reactions from Tokyo, Seoul and the United States have been on the theme: “We’ve heard all that before,” coupled with demands for North Korea to prove it is serious about giving up its nukes.

But North Korea keeps on adding sweeteners without actually offering any concessions. On Wednesday, the North reopened a hotline linking North to South Korea at Panmunjom, the “truce village” on the line about 40 miles north of Seoul where the Korean war armistice was signed in July 1953.

Chinese officials in Beijing have fully supported North Korea’s call for talks, and China’s President Hu Jintao is expected to repeat that call when he meets U.S. President Barack Obama in Washington next week. Gates has hedged bets by saying there’s “urgency to proceeding down the track of negotiations and engagement” while also saying North Korea must do something “concrete.”

The persistence of North Korean pleas to talk leaves analysts wondering what it is the North really wants.

One obvious guess is that North Korea needs food and fertilizer while its people are suffering through another harsh winter. South Korea during the decade of liberal leadership before the election of the conservative Lee Myung-bak sent more than half a million tons of aid each year, but Lee stopped the shipments amid demands the North give up it nukes.

Another theory is that North Korea’s ailing leader, Kim Jong Il may need a respite from tensions while worrying about his dream of having his youngest son, Kim Jong Un, succeed him.

Kim Jong Un observed a birthday on Jan. 8 — his 28th or 29th, no one knows for sure which — but it was a low-key affair.

“There were lectures and messages,” said Ha Tae-kung, whose short-wave radio station broadcasts news into North Korea, “but a big ceremony was not appropriate" and might generate “negative emotions.”

"The North Korean media did not report the birthday," said Ha. “They are really afraid something might happen.”