The sudden departure of Japan's popular foreign minister could prove to be political trouble for Prime Minister Junichiro Koizumi. Voters may see the ouster of the outspoken Makiko Tanaka as a return to politics as usual.

The sudden ousting of Japan's leading female politician shocked many Japanese and left them wondering about the government's direction.

Prime Minister Junichiro Koizumi requested Makiko Tanaka's resignation late Tuesday, after her escalating feud with a deputy took center stage in parliament, distracting legislators from debate on a much-needed economic stimulus package.

Politics professor Roger Buckley, at International Christian University in Tokyo, says the move could be costly for the prime minister.

"I think many Japanese would say that it is the end of what has been a very prolonged honeymoon for Mr. Koizumi," said Prof. Buckley. "He has been able to ride so high in the opinion polls that inevitably sooner or later there was going to be a bump and he would come down to earth. The fact is he is been very severely embarrassed by having to fire his closest confidante in the cabinet."

Support from Ms. Tanaka, the 57-year-old daughter of a former prime minister, helped Mr. Koizumi win the country's top post last April. Surveys show that Mr. Koizumi has maintained strong public standing, with at least 70 percent of the people backing him and his plans to reform Japan's troubled economy.

But analysts say ousting Ms. Tanaka is risky because Mr. Koizumi has broken a public vow to retain his cabinet ministers as long as he stayed in office.

Professor Stephen Reed of Japan's Chuo University says the move also could damage Mr. Koizumi's image as a reformer who eschews the factional power-broking for which his ruling Liberal Democratic Party is famous.

"The thing to remember is that Mr. Koizumi is popular because he represents the new LDP, not the old LDP. Firing Ms. Tanaka makes him look like the old LDP," said Prof. Reed.

Ms. Tanaka herself established a reputation years ago as a maverick within the ruling party. She often made fun of other politicians, and when she became the country's top diplomat she vowed to rid Japan's Foreign Ministry of what she called arrogant and corrupt practices. But from the start, she was at odds with senior bureaucrats and was criticized by senior LDP members.

Her difficulties became an ongoing saga in Japan's tabloid newspapers as her enemies leaked stories to reporters. For instance, Ms. Tanaka was accused of missing a meeting with a visiting dignitary because she had lost a piece of jewelry. She was also reported to have erupted angrily when she was not invited to a party held by the Japanese Emperor.

Whether or not the stories are true, Professor Reed says she appeared distracted from the business of running the Foreign Ministry.

"She was not doing a great job running the Foreign Ministry or Japan's foreign affairs. There were lots of problems with her," said Mr. Reed. "If Mr. Koizumi can find something else for her to do and continue to keep her support it is not such a horrible thing. On the other hand, if he drops her and she becomes an enemy of the Koizumi regime, she can cause an awful lot of trouble."

While Mr. Koizumi attempts to ease Japan's Foreign Ministry through a change in leadership, he now may come under more pressure than ever to retain public support and make real progress on reviving the country's ailing economy.