TOKYO -- Japanese Prime Minister Toshiki Kaifu, widely derided as a weak, lame-duck leader when he took over last summer, has confounded the experts and soared to unexpected popularity in recent polls.

A nationwide survey conducted this month by the Japanese news service Kyodo showed Kaifu with a 63 percent popularity rating, the highest of any prime minister since it began polling in 1964. A recent television poll and an earlier survey by the independent newspaper Yomiuri Shimbun also found surprisingly high approval ratings.

Kaifu's surging popularity has strengthened his position at home and in his dealings with the United States. More placid relations with the United States have contributed to his high approval rating.

Politicians and analysts say that Kaifu's surging popularity figures indicate he will last as prime minister at least through the fall, when Japan will host dozens of national leaders for the official enthronement of Emperor Akihito, and probably longer.

According to analysts, people here have responded positively to Kaifu's relative youth at age 59, his forthright speaking manner, clean image, stated determination to reform Japan's corrupt political system and ability to resolve trade tensions with the United States at least temporarily.

President Bush's recent meetings with Kaifu and telephone calls over trade problems have buoyed the prime minister by giving the impression that the United States -- Japan's most important ally -- takes Kaifu seriously, analysts said.

In addition, Kaifu has been boosted by the perception that he is an underdog, with ambitious party heavyweights plotting to manipulate him, force him into a bad light or knock him from the prime minister's post.

Kaifu was a little-known politician from a minor faction of the ruling Liberal Democratic Party when he was thrust into the top leadership role last August by party barons unable to find a more senior politician untainted by money and sex scandals.

It was hoped that Kaifu would give the party a new image, in the wake of a trouncing in July's upper-house elections and before it faced a more important contest for the lower house. Newspaper headlines at the time labeled him a "front man" and a "puppet," whose ability to stay in power was dependent on the whim of more powerful men behind the scenes, primarily ousted prime minister Noboru Takeshita.

Few politicians or analysts expected Kaifu's government to last much beyond the lower house elections in February. But the ruling party's success in that contest and Kaifu's soaring popularity since then have squelched discussion of an imminent change.

According to Kyodo News Service, Kaifu's 63 percent popularity rate was the first time a prime minister had topped 60 percent. The previous record was held by Yasuhiro Nakasone, who had a 59.6 percent popularity rate in a September 1985 Kyodo poll. However, Nakasone, who was embroiled in the so-called Recruit insider trading scandal, saw his popularity evaporate. He had difficulty winning reelection to the parliament in February and has since kept a low profile nationally.

Takeshita had the second-highest popularity rating, with 59.6 percent of those surveyed backing him as prime minister in November 1987. Takeshita's popularity plunged after it was revealed that he, too, was involved in the Recruit scandal. He made history with the lowest popularity rating recorded in several Japanese polls and later resigned.

The Yomiuri poll, conducted at the end of April, also showed Kaifu's popularity rising quickly. However, former prime minister Kakeui Tanaka, convicted in another money scandal, still held the record for the highest popularity rating, according to the newspaper survey.

Born: Jan. 2, 1931

Elected Prime Minister: Aug. 9, 1989

Professional life: Kaifu's entire working life has been spent in politics, first as an aide to the Diet, the lower house of Japan's parliament, later as a Diet member. He was elected 10 times, serving twice as education minister and deputy chief cabinet secretary.

Background: Kaifu is the second-youngest premier in the country's postwar history and the first prime minister too young to have served in World War II. Under normal circumstances he would not have become prime minister so soon, but scandals disqualified or destroyed the chances of other party leaders.

SOURCE: Who's Who in Japan, The Washington Post