TOKYO, AUG. 10 (FRIDAY) -- The first sign that Toshiki Kaifu might be a surprise as Japanese prime minister came a year ago today, when the obscure backbencher was catapulted into the job of chief executive of the world's second-richest country.

Setting out for his first day as head of government, Kaifu came walking out of his apartment with his wife, Sachiyo, at his side.

That was the tip-off. "All the prime ministers before him used to walk two or three steps ahead of their wives, to assert their status," says Testuo Kondo, an ally of Kaifu's in the Liberal Democratic Party, which dominates the Diet, as the Japanese legislature is called.

"But Kaifu was willing to show that his wife is his equal. And that appeals to something that is new in Japan."

By aiming his politics directly at new elements in this fast-changing society -- at women clamoring for a more equal role, at consumers demanding a bigger stake in the nation's enormous wealth, at young people who want to see Japan treated as an equal by the United States and other allies -- Kaifu today completes a successful first year in office with approval ratings that are astronomical by Japanese standards.

In various surveys, Kaifu's approval rating runs between 56 and 60 percent. No Japanese prime minister has ever scored higher in opinion polls.

The irony in all this is that Kaifu was generally considered a hopeless case when he got the prime minister's job -- purely by default -- last August. The Liberal Democratic Party (actually the most conservative of Japan's major parties) was desperate because its two previous leaders had both been forced to quit because of scandal. Kaifu was the only LDP member of the Diet left who was young enough and clean enough to succeed to the prime ministership.

With minuscule name recognition and minute support in his faction-ridden party, Kaifu was expected to spend a brief, troubled period in a caretaker role, serving as front man for more powerful figures. As soon as he got to the prime minister's seat, though, Kaifu began rewriting that script.

The 59-year-old lifelong politician asserted himself with particular force in foreign affairs. Building a personal friendship with George Bush, he skillfully managed to exploit that relationship here by not appearing to be under the president's thumb. When Kaifu agreed, for example, to accept unprecedented U.S. demands in trade talks, he came home and adroitly sold the move as a great breakthrough for the interests of Japanese consumers.

Kaifu scored a personal triumph in foreign affairs at the Houston summit last month in an incident that crystallizes this nation's acute self-consciousness about its proper role on the world stage.

On the afternoon of July 7, the heads of state of the developed nations took a break from their meeting for a photo opportunity. While they were standing around, Kaifu poked Canadian Prime Minister Brian Mulroney in the ribs and told him a joke about the humidity in Houston. Mulroney laughed.

It was all over in the blink of an eye. But those few feet of videotape have been shown over and over in Japan. Here at last was a Japanese leader comfortably situated as a peer with the titans of the West. Sanpei Sato, editorial cartoonist for the giant Asahi Shimbun newspaper, proposed that July 7 become a holiday called "Kaifu Memorial Day" because on that day, Western leaders had actually paid attention to a Japanese prime minister.

Despite the overseas success, and despite Kaifu's triumph in leading his party to a major victory in last February's national election, the prime minister gets almost no respect from many leaders of his own party. Indeed, it is quite possible the LDP will dump Kaifu when he comes up for a second term in 1991.

"The man has no policy, no ideas," says Takayoshi Miyagawa, an influential political consultant who advises, and speaks for, several of the biggest guns in the LDP.

"Kaifu got where he is by luck," Miyagawa continues. "He's had a lucky year because things are going right. But those poll ratings -- that's like a glider in the wind. Nothing is holding him up. With the first down-draft, he'll crash."

As befits a nation that is obsessed with golf, many of the first-year-in-office assessments appearing in Tokyo these days use golfing metaphors. Thus former prime minister Noboru Takeshita, also a member of Kaifu's party, dismissed the current leader with the comment that Kaifu has been "playing in a tail wind," but that the wind could shift and blow against Kaifu at any time.

Because of his reported friendship with Bush, Kaifu is often compared here to the current U.S. president. In some ways, though, the closer resemblance is to Ronald Reagan.

Like Reagan, Kaifu is popular with ordinary folks, but earns disdain from policy professionals in the capital. Reagan biographer Lou Cannon has said the ex-president benefited from the fact that he was often underestimated. The same is true for Kaifu, who has handled the reins of power with far more finesse than anyone predicted.

Like Reagan, Kaifu is accused of being manipulated by his wife and his staff. In political circles, Sachiyo Kaifu and the prime minister's chief aide, Shozen Kaneishi, are known by the nicknames "Do This" and "Do That" because they are believed to boss the prime minister around.

And like Reagan, Kaifu has a way of overcoming the political intrigue of Nagatacho -- a Tokyo region roughly equivalent to "inside the Beltway" -- with an electrifying ability to appeal to ordinary voters on an intensely personal level.

This week, for example, Kaifu traveled to both Hiroshima and Nagasaki to commemorate the atomic bomb blasts of 45 years ago.

In Nagasaki, the prime minister found his way to a nursing home for survivors of the nuclear explosion, where the patients lined up in their wheelchairs to meet him. In moving and evidently heartfelt terms, he told the elderly audience how deeply he felt their pain and sorrow.

In a matter of minutes, relating his own wartime experience as a teenage conscript factory hand in an airplane engine plant, Kaifu captured the crowd. By the time the visit was over, the patients were crying, Kaifu was crying, and a deep sense of camaraderie between politician and people pervaded the room.

Kaifu has yet to find a formula for converting his popularity with voters into respect within the ruling party. If he fails to do that by next summer or so, the party may pick a new prime minister, regardless of Kaifu's popularity ratings.

Being replaced is an eventuality Kaifu clearly wants to avoid because he has grown comfortable in the job he got more or less by accident.

A year ago today, when Kaifu first heard reporters address him as "prime minister," he was so abashed that he asked the pack to continue calling him "Kaifu-san." Last month, though, one reporter did use the name "Kaifu-san." This time, Kaifu was furious. "I don't know who you mean by 'Kaifu-san,' " he snapped. "But from now on, you'd better get used to calling me 'prime minister.' "