Princess Kiko is pregnant, the Imperial Household Agency said Tuesday, just as the government considered a plan to allow women to assume the throne for the first time in two centuries in a bid to avert a succession crisis.

The announcement raises the possibility of the birth of the first male heir to the Chrysanthemum Throne in 40 years. Kiko's husband, Prince Akishino, is second in line to the throne.

Agency chief Shingo Haketa said both Emperor Akihito and Empress Michiko were delighted by the news of Kiko's pregnancy.

The princess had an ultrasound Tuesday morning and felt the fetus move, Kyodo News agency reported, adding that Kiko was expected to give birth in September or October. Kyodo cited imperial agency sources it did not identify.

The news prompted applause at a parliamentary committee meeting attended by Prime Minister Junichiro Koizumi earlier in the day as Japanese media began reporting on the pregnancy hours before the imperial agency announcement.

"We'd like to celebrate the news with the people," said Katsuya Okada, a member of the opposition Democratic Party of Japan.

Kiko, 39, has two daughters, aged 14 and 11. Crown Prince Naruhito, first in line to the throne, has one daughter with his wife, Crown Princess Masako. Enormous pressures to produce a male heir and adjust to palace life contributed to a stress-induced condition that caused Masako to withdraw from public activities in December 2003.

The lack of a male heir has prompted the government to consider changing a 1947 law so Naruhito's 4-year-old daughter, Aiko, could one day take the throne. The current law allows only males to reign.

Koizumi called for early consideration of the popular measure, despite criticism by conservatives and the new prospect of a male heir being born.

"If we wait, it is uncertain that a boy may or may not be born," he told lawmakers.

"To ensure the stable continuity of Japan's imperial family, we cannot put the issue off any longer. It is desirable that parliamentary debate is carried out in a calm, careful manner at the earliest opportunity."

The proposal, however, has ignited a wide-ranging debate in Japan.

Conservative opponents argue that allowing a woman to reign — and pass the throne to her offspring — would corrupt a millennia-old Japanese tradition, which they say is based on the maintenance of the male lineage.

Under those restrictions, a son delivered by Kiko would provide a suitable male heir.

Some critics have called for bringing back imperial concubines — as were used until the early 20th century — to breed male heirs. Others say the wider aristocracy, banned after World War II, should be reinstated to widen the pool of candidates for the throne.

The royal family's duties are mostly ceremonial, convening parliament and hosting heads of state but staying out of Japanese politics. It also is involved in charitable efforts.

Okada urged a cautious approach to Koizumi's proposal, saying it would be "too hasty" to push it through the current parliament.

"I find it really awkward. For the future stability of the royal family, we should give enough time to allow more thorough discussion," he said.

In the 1,500 or so years that Japan's royal family has reigned, only eight empresses have ruled. The most recent was Gosakuramachi, who ascended the throne in 1763. The practice over the centuries has always been to use men whenever possible, and the 1947 law codified the tradition.

Last month, at the annual imperial verse reading ceremony, with its theme on children, both Akishino and Kiko wrote about storks.

The agency denied the poems indicated the possibility of the couple having a third child, saying they were simply recalling a visit to a ceremony last year in which protected storks were released into the wild.

Baby goods stocks jumped following the reports of Kiko's pregnancy, although the benchmark Nikkei was slightly down.