To ritual cries of "Banzai!" Emperor Akihito ascended the High Throne of Japan Monday in a pageant watched by kings, princes and political leaders from 158 countries.

Akihito, who according to legend is a direct descendant of the Sun Goddess, pledged in a brief address to honor the country's post-war constitution which relegates the once all-powerful role of the emperor to a mere "symbol of the nation."Prime Minister Toshiki Kaifu led ministers and courtiers in the traditional shouts of "Banzai!" which translates "may you live ten thousand years!"

Unknown to the imperial family and the 600 state guests within the palace moat, who heard only the distant sound of sirens, leftist radical groups staged attacks with homemade missiles and fire and smoke bombs in and around the capital.

As the enthronement got under way, five crude projectiles landed on the pavement near the posh Ginza district, only about half a mile from the palace, and 200 yards outside the moat.

It was a crisp, sunny day in Tokyo, and citizens enjoying the national holiday had been expected to throng the route Akihito and his empress were to travel by motorcade through streets near the palace.

Perhaps because of the guerrilla attacks, or the pervasive security, the crowds along the route appeared sparse, an estimated 75,000 instead of the projected 300,000.

In the palace courtyard where the enthronement took place, such worries seemed to belong to another world.

Autumnal sunlight flooded the scene, bright with ancient multi-colored banners and the archaic uniforms and symbolic feathered arrows, lances and swords of the imperial guards.

High state officials and foreign dignitaries took their places in the courtyard, among them Vice President Dan Quayle, Britain's Prince Charles and Princess Diana, Belgium's King Baudouin and Queen Fabiola, and more than 50 national presidents.

Akihito and Empress Michiko, both 56, then took their places on curtained thrones, unseen by the guests outside.

To the sound of gongs, the curtains were pulled back to reveal the imperial couple seated side by side on high, roofed thrones in brightly lacquered wood.

The emperor wore a chestnut-brown silk robe with deep sleeves and a black headress with soaring plume. His consort wore a multilayered kimono.

Imperial family members at the ceremony were led by Crown Prince Naruhito, 30. Dowager Empress Nagako, widow of Emperor Hirohito who died in January 1989, is too frail to appear in public.

Thumbing their noses at the massive security force arrayed against them - 37,000 police, bomb-sniffing dogs, helicopters and an observation balloon - radicals struck some two dozen times up to midafternoon.

None of the attacks on army camps, shrines and subways caused any injuries, and the palace ceremonies went ahead without disruption.

Fires broke out on three subway trains, at least two apparently sparked by incendiary devices. Earlier, rudimentary missiles were fired at four Japanese army camps around Tokyo. Another harmless projectile landed at the U.S. Navy air station at Atsugi, west of Tokyo.

Two religious shrines in Tokyo went up in flames and fires alongside rail lines and in one subway station halted some train services in the capital. In yet more incidents, projectiles were fired at a police hostel near Ginza and at Narita Airport outside Tokyo.

Japan's radical left opposes the enthronement on the grounds that the pomp and pageantry hark back to a military past when imperial troops invaded and repressed many Asian nations in Hirohito's name.