As more than 3,000 courtiers, dignitaries, guests - and a horde of French photographers - looked on, former President-for-life Jean-Bedel Bokassa placed a jewel-encrusted crown on his head today and became Emperor Bokassa I of the Central African Empire in one of the most lavish ceremonies in recent world history.

The toga-clad emperor then crowned his No. 1 wife, Catherine, amid trumpet fanfares from a visiting 60-member French army bad, as thousands of Bokassa's subjects watched the flittering coronation in this steamy riverside capital.

The ceremony, which was scheduled for 9 a.m. began more than an hour late as several hundred diplomats and dignitaries trickled into the coronation palace. Bangui's modern indoor sports stadium. It had been decorated with hundreds of yards of crimson bunting, flaggs, and a two-ton, gilden throne in the shape of aperched eagle with a wingspan of nearly 12 feet.

Bokassa thus became Africa's first years ago, and its fourth monarch. Swaziland, Lesotho and Morocco all kingdoms, are Africa's only other monarchies. The ceremony was attended by Sir Seerwoosagur Ramgoolan, president of Mauritius, and by the Prince of Liechtenstine. Dozens of other official delegations were led by ministers and officials.

The eleborate coronation ceremony and tonight's gala dinner will cost at least $25 million. The Central African Empire is officially listed as one of the world's 25 poorest nations, with an annual per capita income of only $155.

Aides to Bokassa said the spectacular coronation was in part aimed at drawing both investors and tourists to the land locked country, which now depends chiefly on coffee, cotton and diamonds for its meager annual foreign exchange earnings of approximately $100 million.

The emperor arrived for the coronation preceded by a brass military band shortly before 10:30 a.m. in a green coach with gold emblems and five gold eagles on the roof. The coach was drawn by six white horses and escorted by about 30 members of the mounted imperial guard.

Bokassa was met at the coronation palace by hundreds of colorfully dressed dancers, several thousand citizens, and another imperial honor guard of sabre-bearing soldiers in cocked hats.

Apart from the ceremonial troops, thousands of additional gendarmes, paratroopers and soldiers were pressed into service to guard the sports stadium, the emperor and his assorted guests. The security forces were armed with Soviet AK-47 rifles and Israeli Uzi submachine guns.

In a separate, open coach preceding the emperor was his two-year-old son, the crown prince. The little prince, wearing a tiny, while military uniform, was escorted into the hall by palace guards and took his seat on a broad, scarlet-carpeted dias to the right of his father's throne. The prince was followed by Empress Catherine, whose 20-foot train was carried by a dozen ladies-in-waiting.

The empress wore a sparkling gold sequin gown and a delicate, gold coronet. Her ladies-in-waiting wore gowns of peach, white, rose and pink chiffon, and broad-brimmed white straw hats.

Then, as the French military band struck up a fanfare, the emperor entered, wearing a toga-like white robe with gold brocade and a golden garland. He walked ceremoniously down the center aisle amid a standing ovation. His 30-foot scarlet train, trimmed with ermine, was carried by yet another honor guard. Minutes after he had taken his place at the throne, an army general strode onto the dais bearing the imperial crown.

Bokassa slowly lifted it, hesitated for a moment, then placed the huge crown on his head, drawing more applause. Shortly afterward, the empress, whose canopied throne was below and to the right of the imperial throne, was crowned by the emperor with a diamond tiara. The young crown prince sat patiently all through the ceremony.

After the coronation, an official procession went a mile to Bangui's Roman Catholic Cathedral of Notre Dame for a solemn high Mass. The emperor rode most of the way to the cathedral in a limousine, but switched back to his coach 400 yards from the church, riding with the empress through a triumph arch to a huge, red marquis with a hundred-foot red carpet at the cathedral door.

After the Mass, and for most of the day, the emperor was thronged by cameramen. During the recessional from the church to his waiting limousine, photographers pressed to within three feet of him, as soldiers in camouflage uniforms tried desperately to control them.

At one point, the emperor stopped as phothgraphers pressed closer. He grabbed a soldier by the arm and said firmly, "leave the press alone,"then let a small creep across his lips.

It was the only time all day the emperor showed any visible emotion.

It is not known how many of the emperor's 2,000 specially invited guests came, Bangui's half-dozen good hotels were packed, and taxis were difficult to find. Motorcycle escorts have been scurrying about Bangui's broad, treed-lined avenues that are now bedecked with banners and lights for the coronation.

There was concern that so many of the empire's two million residents would troop to the capital for the ceremony that national police were told to cordon off Bangui Thursday. Still, as the emperor drove from the cathedral to the Renaissance Palace after the Mass, thousands of women in grass skirts, singing and dancing, greeted him.

The emperor left his car several hundred yards before the palace and walked through the crowds, protected by a horde of soldiers.

A reception followed for the more than 40 delegations, uncluding both North and South Korea, the Soviet Union and China, Israel and Lebanon, and even Nepal. The United States w as represented by its resident ambassador, Anthony Quainton.