By Jane Macartney

LHASA, China, Oct 1 (Reuter) - Computerised cameras and shabby museum guards sliding over ancient floors on pads of goatskin combine to protect the costliest renovation China has ever undertaken.

Tourists jostle with Tibetan pilgrims to view the sumptuously decorated palace that was for 400 years the winter home of the Dalai Lamas, the god-kings who held spiritual sway and sometimes temporal power over this remote Himalayan region.

Beijing pumped 53 million yuan ($6.4 million) into its five-year renovation of the soaring Potala Palace, with its labyrinth of countless rooms, that towers over Lhasa, capital of this remote Himalayan region.

"It is the most expensive renovation that the central government has ever undertaken in China," Qiong Da, deputy director of the Potala Palace Management Committee said in an interview.

"When I first came to work in the Potala Palace in 1985 all the pillars were leaning over and propped up by poles," he said.

"I was very troubled because I never knew if the Potala Palace was going to collapse today or tomorrow," he said.

China undertook the first restoration of the palace since the 17th century, not because it anticipates the swift return of the 14th reincarnation of the Dalai Lama, who now lives in exile in India following an abortive anti-Chinese uprising in 1959.

The investment, initially calculated at 35 million yuan ($4.2 million), was motivated by official realisation of a need for a way to placate Tibet's influential and often restive monks and by the prospect of luring more tourist dollars to China's remote, backward and mysterious Shangri-la.

Tibet has been rocked by repeated anti-Chinese protests that Beijing charges are stirred up by separatist supporters of the Dalai Lama, won the Nobel Peace Prize in 1989 for his peaceful campaign for autonomy for his Himalayan homeland.

Under roofs of gold leaf that can be seen glittering in the sunlight from miles away across the plain that surrounds Lhasa, Chinese experts and Tibetan workers and monks have completed one of the most extensive restorations of a historic monument ever attempted in China.

Much of the building of the central religious Red Palace and the surrounding secular White Palace was undertaken by Tibet's Fifth Dalai Lama who moved there in about 1650.

The Fifth Dalai Lama's spectacular architectural achievement was constructed around the surviving rooms of a fort built by a Tibetan king in the 7th century AD.

Restoration presented an awesome challenge to artisans struggling to return the palace to its former splendour while trying to recreate the materials used hundreds of years earlier, Qiong Da said.

The palace had been ravaged by natural erosion of its stone and earth structure and by infestations of insects that had gnawed their way through most of its hundreds of pillars and almost all of its thousands of wooden window frames.

"We had to get rid of the huge number of dangerous sites, like all those beams," Qiong Da said, gesturing to the huge wooden struts arching across the ceiling of the main throne room of the Dalai Lamas.

"One basic principle was that we would not change the original, we would not use any modern materials," he said. "Whatever was there before, we would keep that."

The task was daunting.

"We started to compile an accurate count of the number of rooms in 1984," he said. "We started with the Red Palace and we are about one-third of the way through now. We have counted about 2,000 rooms but we think there may be as many as 7,000."

One of the greatest challenges was to recreate the ochre mortar that was used to build the floors and flat roofs of the palace, he explained.

"This was a very arduous task because the quality does not meet the original," he said. "We studied this very carefully and in the end we believe we were successful because we achieved about 70 percent of the quality of the original."

It was time-consuming work.

"In those days, people had unlimited time to do this work," he said.

More than two years after the restoration was completed amid great fanfare from its Chinese financiers, two Tibetan women sat on the roof and used a centuries-old method to tap water with flat wooden spatulas into newly laid mortar.

The government has tripled annual allocations for palace upkeep since the completion of the restoration, installed the latest in a computerised system of cameras to monitor the treasures of each room against theft and guards glide across floors on scraps of goatskin to protect the mortar from their hard leather-soled shoes.

Palace workers are installing glass walls around the bases of the jewel-encrusted stupas that house the mummified bodies of eight Dalai Lamas. The glass is intended to wall out the mice that devour the layers of decorative gold leaf flavoured by aromatic smoke from yak butter lamps offered by centuries of pilgrims.

"We are always renovating and working to keep up the restoration," said Qiong Da.