BANGKOK -- Thailand's beloved King Bhumibol Adulyadej turns 60 today after 41 years on the throne. Amid the pageantry of the celebration, there is an unspoken sense of foreboding about the future.

Known here simply as "the king," the talented Bhumibol is seen by many Thais as an ideal monarch. He is an accomplished painter, a noted jazz saxophone player, photographer, sportsman, symbol of national unity and embodiment of Buddhist religious values.

Recently, he has been seen as a source of legitimacy for military-backed governments and the final arbiter among the competing political factions of Thailand's complex political system. In 1985, Bhumibol exercised his moral authority by refusing to support an attempted coup d'etat, which consequently failed.

Analysts say the king maintains a commanding presence over Thailand's political development in part because he does not interfere in its course. "One reason he has survived so long is that he has stayed above the political fray, only stepping in when there's a crisis," said one diplomat here.

"The king has never meddled in politics on a day-to-day basis," said Sukhumbhand Paribatra, a Chulalongkorn University political science professor.

As a result, the king has become enormously popular, with his picture adorning every public and private building, every office, every village hut. So revered is the king that any hint of a slur is considered an intolerable offense. One who learned that lesson is Veera Musigapong, once an influential member of parliament, deputy interior minister and secretary general of the Democrat Party. A court this fall sentenced Veera to two years in jail for insulting the monarch.

During the July 1986 election campaign, Veera was quoted as saying he wished he had been born to royalty so he could get up late in the mornings and not have to work so hard. Veera was forced from parliament and prosecuted despite standing before a portrait of the king in the assembly hall and performing a ritual of atonement.

The king's birthday has prompted questions about whether any future monarch without the current king's popularity would be able to play a similar role in Thailand.

"It's a compliment to the current king that he has put himself on an equal footing with the monarchy itself," Sukhumband said. "If he is no longer there, the institution may suffer."

Because of the extreme sensitivity of questions of the monarchy, Thais and foreigners are reluctant to talk openly about the succession. But, with the king having hinted that he might abdicate his throne to become a Buddhist monk, many Thais are concerned about how their country would fare without him.

The heir to the throne is Crown Prince Maha Vajiralongkorn, a major general in the Royal Thai Army who recently became commander of a regiment based in Bangkok. The crown prince has reportedly told interviewers that he views himself as a professional soldier and sees no conflict between his roles as a future monarch who must arbitrate between the factions and a military leader in his own right.

A few years ago, the royal family was reportedly concerned about the prince's image as a playboy. Lately, however, the crown prince has been attending more official ceremonies, appearing frequently on the front pages of Bangkok's newspapers. He has also taken some highly publicized official trips abroad.

While most of the trips went well, a recent visit to Japan ended in controversy when the crown prince complained that he had been treated in an unroyal manner.

For all of the king's popularity and political importance, the monarchy was an irrelevant institution for the first decade of his reign, which began in 1947 after the mysterious killing of his older brother. After young colonels overthrew the absolute monarchy in 1932, the kingdom was eclipsed by a succession of military governments.

In 1957, when strongman Sarit Thanarat became prime minister, he apparently set about reviving the moribund monarchy as a way to legitimize his own position. The king was allowed more freedom to travel, and royal ceremonies that had fallen by the wayside were revived.

The king "never looked back," said one Thai observer. "The monarchy developed its own momentum."