With speeches, songs and the traditional three shouts of "banzai," or "ten thousand years," official Japan today marked another milestone in the reign of Emperor Hirohito -- its 60th year.

About 5,000 leaders of government, business and society gathered in the national sumo wrestling stadium here to honor the emperor, who sat before them beside his two sons and a bonsai tree, and to acclaim the long reign that the Japanese call Showa, the Era of Enlightened Peace.

"Looking back over the 60 years of Showa, and thinking of the sacrifices of the people in the previous war, my heart still suffers and I strongly feel the preciousness of peace," Hirohito said in brief remarks to the gathering.

"It is very impressive that through the efforts of the people, my country has developed remarkably after many difficulties and made possible the stability and prosperity of the life of people today," he said.

The ceremony, held on the emperor's 85th birthday, was the centerpiece of a series of celebrations being held this year to mark Hirohito's 60th year on the throne. The 60th anniversary of his accession is Dec. 25.

Prime Minister Yasuhiro Nakasone led the emperor in a procession into the stadium and, in a brief speech recounting the history of Showa, called his longevity on the throne a "rare happy event in history."

Hirohito received the praise from Nakasone and other dignitaries passively, showing animation only when he applauded a medley of Japanese songs composed during his reign and performed today by a children's choir.

Before the ceremony, about 63,000 people trooped into the grounds of the Imperial Palace in central Tokyo in the annual opening of the gates for his birthday. He and members of the imperial family appeared to the crowds four times from behind bullet-proof glass.

The emperor met with the palace press corps in a formal interview, saying the war was the most unpleasant period in his reign and expressing hope that the economic summit to be held in Tokyo from May 4 to 6 will be a success.

He credited his long life to respecting his physicians' views and eating the correct amount of food, the Japanese news service Kyodo reported. He said he gets a fair amount of exercise and tries to live his life according to a fixed schedule.

At the stadium this afternoon, Hirohito received several dozen people who were born in the seven-day period Dec. 25-Dec. 31, 1926, which by Japanese count was the first year of the reign. On his way out, two children gave him bouquets and he said to each of them: "Work well and be a good child."

Hundreds of helmeted riot police stood outside the stadium to guard against leftist groups that, calling Hirohito a symbol of government oppression, had threatened to disrupt the occasion.

This morning, people identified by police as leftist radicals briefly cut some rail lines in Osaka city and the high-speed train line between Tokyo and Osaka by sabotaging electrical and communications cables.

There was no disruption at today's ceremony, but police said that about 4,600 leftists rallied at five places in the city to protest it. Thirteen were arrested on charges of obstructing traffic and police business.

The ceremonies also came under fire from the opposition Japan Socialist Party and Japan Communist Party which charged that Nakasone scheduled the celebrations at this time to use the emperor to build political capital for himself.