Princess Masako, whose pregnancy was trumpeted in the Japanese news media this month, has had a miscarriage, according to Imperial palace officials.

The announcement dashed Japanese hopes for now of a millennial baby who could extend the reign of what is called the world's oldest hereditary monarchy. Japan's Crown Prince Naruhito, who is next in line to become emperor, and his American-schooled wife have yet to produce an heir after six years of marriage.

The "signs of pregnancy" by Masako had been reported in huge banner headlines, "extra" editions of the Asahi newspaper and breathless broadcast reports three weeks ago. The topic was the talk of the country, and coverage was so overheated that there were stories about whether the new baby might revive Japan's flat economy.

But after an earlier pregnancy test was said to be inconclusive, doctors yesterday reexamined Masako, 36. They said she had suffered a common miscarriage and there was no fetal heartbeat. She remained in the hospital for a procedure to remove the unsustained embryo, according to Takashi Okai, head of the Aiiku Hospital gynecology department.

The announcement will be met glumly in Japan, where the failure of Masako and Naruhito, 39, to produce an heir has been watched intently even by those who profess little interest in the ceremonial royal family.

The miscarriage also is likely to rebound on the news media here, which have been periodically vilified for putting "pressure" on Naruhito to find a wife and then on Masako to produce offspring. In fact, the media have gone through periods of self-enforced silence on those matters, but the dam-break of stories this month -- clearly fed by palace "sources" -- prompted more scolding by the Imperial Household Agency.

Okai said such "pressure" or stress had nothing to do with the miscarriage, which is not uncommon in early stages of pregnancy. He said Masako probably was about seven weeks into the pregnancy. There is no impediment to her becoming pregnant again, Okai said. He said he would recommend that the princess wait a month before resuming her official duties.

Naruhito, the eldest of three children of Emperor Akihito and Empress Michiko, was said by the palace agency to have been "calm" when he received the news from the physicians.