In the 1980s, flush with oil wealth and eager to show it, the Saudi royal family erected a magnificent new public building to celebrate the arrival of the ultra-modern Saudi capital on the world stage. Fittingly, it was a concert hall.

By all accounts, the King Fahd Cultural Center is one of world's most technologically sophisticated performance halls, with laser lighting, seating for more than 3,000 people and a hydraulically operated stage. A peek through the locked glass entrance reveals plush salon chairs and a vast expanse of heavily marbled foyer.

But don't go running for tickets.

Because of objections from conservative Islamic clerics -- who fear an onslaught of mixed-sex audiences and operas starring unveiled foreign divas -- the curtain has yet to go up on a single performance since the massive hall was completed in 1989, according to Western diplomats, a European employee and others familiar with its history.

"The reason they never opened it to the general public is they are embarrassed by the whole thing," said a foreign diplomat who was granted a rare tour of the facility, built for an estimated $140 million and still maintained in pristine, air-conditioned splendor by a full-time staff of 180. "They don't want to show they spent so much money on something un-Islamic."

The story of the mothballed performance hall opens a window onto one of the most striking and important aspects of life in Saudi Arabia: the tension between modernization -- which has yielded a familiar First World landscape of silken highways and air-conditioned shopping malls -- and religious conservatism in a society that is, at least to Western eyes, one of the most alien and austere on Earth.

Nowhere is that tension more evident than in Riyadh, one of the world's fastest-growing cities. American restaurant franchises -- Burger King, Wendy's, Kentucky Fried Chicken -- coexist with shrouded women, religious police and occasional public beheadings. Saudi professionals hone their physiques in sleek new health clubs equipped with Stairmasters and prayer rooms.

Westerners often assume that the conservatism of Saudi life reflects government policy -- that Saudi women, for example, would willingly shed their veils if they could do so without fear of condemnation. In fact, the opposite may be true.

While some Saudis would welcome a more relaxed society -- such as one in which women were allowed to drive -- interviews with ordinary Saudis, government officials and foreign residents over the course of 12 days suggest that it is Saudis themselves who insist on strict Islamic standards of public decorum, even if that means doing without a concert hall.

"The conservatism you see in the street is not governmentally ordained," said Aziz Fahd, a Yale-educated Saudi lawyer who was brought up in Riyadh. "It is the other way around."

Because the legitimacy of the Saud family flows from its status as the guardian of the holy shrines at Mecca and Medina, the government must be careful not to offend the Saudi religious establishment, known collectively as the ulema. The ulema's insistence on strict segregation of the sexes is reflected in the public life of the capital, where even the municipal zoo sets aside separate visiting days for families and single men.

But the government takes a more relaxed attitude toward private behavior, tolerating, for example, the widespread use of television satellite dishes even though they are supposed to be illegal. Prince Bandar bin Sultan, the Saudi ambassador to Washington, likes to compare the relationship between the royal family and its subjects to that of two men holding a fine thread: When one pulls, the other yields, and vice versa.

Maintaining that balance is not always easy. Islamic militants have made an issue out of the royal family's pro-Western leanings, winning points with middle-class Saudis feeling the pinch of lower oil revenues. The surge of Islamic militancy in Saudi Arabia -- blamed for two bombings of American military sites in the last 12 months -- has raised fears in Western capitals of a threat to the stability of the world's largest oil supplier.

"This is the twist in this country," said a wealthy Saudi businessman who is close to the royal family. "The government is pushing toward modernization, and the culture is going backward."

Perhaps because of that, the concert hall -- known to Westerners here as "the opera house" -- is something of an embarrassment to Saudi authorities. Officials at the Information Ministry initially professed ignorance of its existence. "Frankly, I've never heard about this," one senior official said. "I mean, for what? Belly dancing?"

A reporter subsequently located the building, a striking edifice of white marble that occupies a barren patch of desert near a busy highway on the outskirts of Riyadh. The building was identified only by a small roadside bearing the initials K.F.C.C. -- for King Fahd Cultural Center.

From all appearances, the hall is ready for opening night. Asian workers tended immaculate flower beds. Sprinklers hissed. In back, near a dozing Saudi security guard, a service entrance opened into the bowels of the facility, where more workers scurried between administrative offices and rooms filled with brand-new machinery.

But in one of the offices, a European employee shook his head when asked if the concert hall had ever been used. "It is forbidden," he said before escorting a visitor to the door. "I don't think it will ever be open."

The employee directed further inquiries to the General Presidency for Youth Welfare, a government agency that is responsible for the facility. But an official at that organization politely turned down a request for a tour. The building is undergoing "modifications," he said, and no opening date has been set.

As pieced together from Western diplomats and a Saudi businessman familiar with the project, the story of the performance hall begins with King Faisal bin Abdul Aziz, who ruled from 1964 until his assassination by a deranged nephew in 1975. Eager to build a modern capital, Faisal envisioned the hall as the centerpiece of a large complex of cultural and sports facilities, according to a person who has seen drawings of the proposed development. But the so-called sports city never came to fruition: Only a swimming-pool complex and the concert hall have been completed.

From the standpoint of its designers, the timing of the project could hardly have been worse. The hall was finished under King Fahd only a year or so before hundreds of thousands of American troops flooded the kingdom to repel Iraq's 1990 invasion of Kuwait, according to several sources.

The presence of the foreign troops on Muslim holy soil -- not to mention the spectacle of female American soldiers in T-shirts driving trucks and carrying guns -- sparked a conservative backlash in the kingdom. Among other things, it strengthened the hand of the religious police, or mutaween, who roam the streets in search of immodestly dressed women and merchants who fail to shutter their stores during five daily prayer periods.

After local religious leaders "went berserk" over the concert hall, the government decided to wait for a more favorable climate in which to open it, said the businessman close to the royal family. Meanwhile, the government is spending large sums to maintain the facility, in which the air conditioning runs constantly to prevent damage to precious interior woods.

In the absence of movie theaters and other public forms of entertainment, Saudis tend to spend their leisure time in the privacy of their own homes. On weekends, especially during spring and fall, middle-class Saudis in Riyadh head for the desert, where many have erected semi-permanent campsites. At least for a Westernized elite, such limited choices can be frustrating. "People are very hungry for entertainment, for having a good time, and there's a lot of money for it, but the problem is the social restrictions," said a Saudi who went to college in the United States and is thinking about moving back there with his family. "It seems like most of the activity is watching satellite television. That's sort of our escape." CAPTION: King Fahd Cultural Center, with a 3,000-seat performance hall, was completed in 1989 but has never been opened.