TOKYO, Nov 17 (AFP) - President Barack Obama's deep bow to Japan's emperor has been castigated by US critics as kowtowing to a foreign leader, but experts in Japanese etiquette praised it as an appropriate show of respect.

Visiting Tokyo last week at the start of his first presidential tour of Asia, Obama bowed down almost at a right angle as he shook hands with Emperor Akihito, the son of Japan's wartime Emperor Hirohito.

The gesture went largely unnoticed in Japan but has sparked intense debate in the United States about whether Obama had disgraced his country by showing excessive deference.

Experts in Japanese etiquette think not.

"Bowing is an expression of respect and open-mindedness as a person greets someone," said Reiko Kasai, chief instructor at JAL Academy, an intercultural training school.

"It is part of a greeting, with which one shows his or her willingness for the meeting," she said, adding that given his height, Obama may have chosen to bow so low to make eye contact with the Emperor.

In Japan, the lower you bow, the more respect you show, from a slight nod of the head to a bow down to 30 degrees and -- the most respectful of all -- a deep bow bending at the waist by at least 45 degrees, experts said.

Bowing can also represent an apology in Japan, where it is not uncommon to see scandal-hit corporate executives doubled over in front of the television cameras to show their remorse for wrongdoing.

The Japanese imperial family, the world's oldest monarchy, lives on the apex of Japanese protocol, and meeting them requires the highest and most sincere demeanor, experts said.

A palace spokesman also played down the controversy, telling AFP that Obama's bow looked "only natural and appropriate."

Akihito is the 125th emperor in a myth-shrouded lineage starting with legendary Jimmu, a descendant of sun goddess Amaterasu, in the 7th century BC.

His father, Hirohito, was Japan's absolute ruler during World War II and only renounced his divinity after Japan's surrender. He died in 1989.

Before meeting the emperor, foreign envoys and visitors are usually told that bowing is important, said Isao Tokoro, professor of imperial studies at Kyoto Sangyo University.

"When visiting a foreign country, it is an admirable international manner to follow the country's own protocol," he said.

"It should be praised and never deserve criticism. In Japan, bowing never means the person underestimates himself."

While some conservative commentators on US talk shows charged that the gesture bespoke a United States that had become weak and overly-deferential under Obama, Japanese media took a more positive view.

"If Obama simply walked up to the emperor and shook hands as he stood tall, he would have looked very arrogant to us," said a Japanese presenter with Nippon Television.

Mami Matsuda, an expert in Japanese etiquette who has written many books on the subject, said Obama seemed to show his affinity to Japan with his bow.

"Shaking hands and nodding would have been enough for the occasion," she said. "He might have intentionally followed the Japanese way."

Meetings with Japanese emperors have often been controversial, especially for the leads of Asian nations where people have bitter memories of Japan's wartime aggression.

South Korean bloggers were infuriated when President Lee Myung-Bak shook hands with Akihito, calling it a disgrace to his own people. (By Harumi Ozawa/ AFP)