A panel on Japan's imperial succession formally recommended Thursday that women be allowed to ascend the ancient Chrysanthemum Throne, a change that could spare the royal family a looming succession crisis.

The panel's final report to Prime Minister Junichiro Koizumi calls for revising Japanese law to give a ruler's first-born child -- of either sex -- the right to head the world's oldest hereditary monarchy. Koizumi has said he plans to submit a bill incorporating the recommendations to parliament next year.

"I think this is an important report which allows for stable imperial succession," Koizumi said.

Japan's imperial family hasn't produced a male heir for 40 years, and Crown Prince Naruhito and Crown Princess Masako's only child is a girl, 3-year-old Aiko.

If approved by parliament, the revision is expected to make Aiko second in line to the throne, behind her father.

"This would be a new experience for the Japanese," said Hiroyuki Yoshikawa, the head of the 10-member panel. "I hope the proposal will receive wide public support and contribute to stable imperial succession."

He said that the proposal was intended to allow Aiko to ascend the throne even if Naruhito and Masako had a boy.

"We intend for the proposal to take effect immediately," he said.

The panel also recommended raising government allowances for single adult princesses to match their male counterparts but said its intention was to make the monarchy more sustainable, not to address gender inequality inside the moat-ringed Imperial Palace.

Strict male succession has been possible only through the use of concubines, a practice that ended during the reign of Emperor Hirohito, who died in 1989 and was the father of the current emperor, Akihito.

Even though nearly half of Japan's emperors were produced by concubines, the practice has become unacceptable by today's standards, the panel said.

It said the current succession law is outdated, considering changes in family values and growing awareness of gender equality over the decades.

Opinion polls have indicated wide support for a ruling empress, but some conservative academics and lawmakers have voiced opposition.

Crown Prince Naruhito, right, with Crown Princess Masako, is first in line to the throne, followed by his brother, Prince Akishino, with Princess Kiko.